When do we need tracks?

- Welcome page (only the video track)
- Conference (depends if starting with audio / video muted is requested)

When do we need to destroy the tracks?

- When we are not in a conference and there is no welcome page

In order to accommodate all the above use cases, a new component is introduced:
BlankWelcomePage. Its purpose is to take the place of the welcome page when it
is disabled. When this component is mounted local tracks are destroyed.

Analogously, a video track is created when the (real) welcome page is created,
and all the desired tracks are created then the Conference component is created.
What are desired tracks? These are the tracks we'd like to use for the
conference that is about to happen. By default both audio and video are desired.
It's possible, however, the user requested to start the call with no
video/audio, in which case it's muted in base/media and a track is not created.

The first time the app starts (with the welcome page) it will request permission
for video only, since there is no need for audio in the welcome page. Later,
when a conference is joined permission for audio will be requested when an audio
track is to be created. The audio track is not destroyed when the conference
ends. Yours truly thinks this is not needed since it's a stopped track which is
not using system resources.

The name better suits its purpose, since it can be called at any time.

Deep/universal linking now utilizes loadURL (when possible). But loadURL
is imperative in the native source code while its JavaScript counterpart
i.e. React App Component prop url is declarative. So there's the
following bug: open a URL, leave the conference (by tapping the hangup
button, for example), and then opening the same URL actually leaves you
on the Welcome page (if enabled; otherwise, a black screen).

The implementation has a flow though: opening the same URL twice in a
row without an intervening leave will leave the first opening and join
the new opening. Which can be improved by not leaving and joining if the
conference is joined, joining, an not leaving. But that can be done
separately as an improvement independent of the current implementation
details.

As https://facebook.github.io/react/docs/typechecking-with-proptypes.html
says, React.PropTypes have moved into the npm package prop-types since
React v15.5. I've already failed to update certain devDependencies
because they mandate the use of prop-types so I'd rather we (gradually
at least) move to prop-types rather than face a lot of work later on.

Avatars are cached to the filesystem and loaded from there when requested again.
The cache is cleaned after a conference ends and on application startup
(defensive move).

In addition, implement a fully local avatar system, which is used as a fallback
when loading a remote avatar fails. It can also be forced using a prop.

The fully local avatars use a user icon as a mask and apply a background color
qhich is picked by hashing the URI passed to the avatar. If no URI is passed a
random color is chosen.

A grace period of 1 second is also implemented so a default local avatar will be
rendered if an Avatar component is mounted but has no URI. If a URI is specified
later on, it will be loaded and displayed. In case loading the remote avatar
fails, the locally generated one will be used.

Web's ExternalAPI accepts an object with properties as one of its
constructor arguments and from which it generated a URL. Mobile's
JitsiMeetView.loadURLObject is supposed to accept pretty much the same
object.

Introduces loadURLObject in JitsiMeetView on Android and iOS which
accepts a Bundle and NSDictionary, respectively, similar in structure to
the JS object accepted by the constructor of Web's ExternalAPI. At this
time, only the property url of the bundle/dictionary is supported.
However, it allows the public API of loadURLObject to be consumed. The
property url will be made optional in the future and other properties
will be supported from which a URL will be constructed.

navigator.product is read-only, so we don't run into the risk of it being
changed.

The end goal of this patch was to avoid opening the camera when there is no
welcome page.

In order to achieve this, the logic for creating the local tracks was
refactored:

Before this patch local tracks were created when lib-jitsi-meet was initialized,
and destroyed when it was deinitialized. As a side note, this meant that when a
conference in a non-default domain was joined, local tracks were destroyed and
recreated in quick succession.

Now, local trans are created and destroyed based on what the next route will be,
and this happens when the target room has been decided. This allows us to create
local tracks the moment we need to render any route, and destroy them when there
is no route to be rendered. As an interesting byproduct, this refactor also
avoids the destruction + recreation of local tracks when a conference in a
non-default domain was left.

React (pun intended) to prop changes, that is, load the new specified URL.

In addition, fix a hidden bug in loading the initial URL from the linking
module: we prefer a prop to the URL the app was launched with, in case somehow
both are specified. We (the Jitsi Meet app) are not going to run into this
corner case, but let's be defensive just in case.

Also expose this in the native SDKs.

It's obsolete now, since config is handled in Redux. Also add a "defaultUrl"
prop so emdedding applications can select what the default base URL is.

The current implementation doesn't use the API and Transport modules. This is
due to the fact that they are too tied to APP at the moment, which is web only.

Once API is refactored and moved into the Redux store this will be adjusted,
though it's unlikely that the lowest level React Native module (ExternalAPI)
changes drastically.

This commit also introduces a stopgap limitation of only allowing a single
instance for JitsiMeetView objects on both Android and iOS. React Native doesn't
really play well with having multiple instances of the same modules on the same
bridge, since they behave a bit like singletons. Even if we were to use multiple
bridges, some features depend on system-level global state, such as the
AVAudioSession mode or Android's immersive mode. Further attempts will be made
at lifting this limitation in the future, though.

The counterpart of the external API in the Jitsi Meet Web app uses the
search URL param jwt to heuristically detect that the Web app is very
likely embedded (as an iframe) and, consequently, needs to forcefully
enable itself. It was looking at whether there was a JSON Web Token
(JWT) but that logic got broken when the JWT support was rewritten
because the check started happening before the search URL param jwt was
parsed.

There were getDomain, setDomain, SET_DOMAIN, setRoomURL, SET_ROOM_URL
which together were repeating one and the same information and in the
case of the 'room URL' abstraction was not 100% accurate because it
would exist even when there was no room. Replace them all with a
'location URL' abstraction which exists with or without a room.

Then the 'room URL' abstraction was not used in (mobile) feature
share-room. Use the 'location URL' there now.

Finally, removes source code duplication in supporting the Web
application context root.

Make 'Add jwt module to react' work on mobile.

* fix(react/participant): store display name in redux

* feat(remotecontrol): Add option to display the authorization dialog in meet

* feat(remotecontrol): Enable ESLint and Flow

The functionality around logging including logging_config.js i.e.
loggingConfig and the other classes and/or functions that initialize
loggers for Jits Meet truly deserves a feature of its own. Start getting
in that direction on both Web and mobile by introducing
features/base/logging and bringing loggingConfig to mobile.

The config object defined by lib-jitsi-meet is not used by
lib-jitsi-meet only, jitsi-meet respects its values as well.
Moreover, jitsi-meet defined classes and/or functions which manipulate
that config object. Consequently, it makes sense to move the config
object and the associated classes and functions in a dedicated feature.

I don't like the file/function name, I'm not excited about the
complexity of the logic it implements, and it's definitely a reusable
piece worthy of being called a utility.

When the audio-only mode is enabled, turn on the proximity sensor to dim the
screen and disable touch controls when there is an object nearby.

Adds translate function with default namespaces and options.

`host` contains the hostname:port portion, whereas `hostname` is just the
hostname, not including the port.

On RN we don't use the global APP object, so don't save the store there unless
it's defined, which is the case in the current web version. Also, check for
undefined explicitly, since a "if (!APP)" check will throw a ReferenceError.