* Button conditionally shown based on if the feature is enabled and available
* Hooks for launching the invite UI (delegates to the native layer)
* Hooks for using the search and dial out checks from the native layer (calls back into JS)
* Hooks for handling sending invites and passing any failures back to the native layer
* Android and iOS handling for those hooks

Author: Ryan Peck <rpeck@atlassian.com>
Author: Eric Brynsvold <ebrynsvold@atlassian.com>

On Android the files will be copied to the assets/sounds directory of
the SDK bundle on build time. To play the "asset:/" prefix has to be
used to locate the files correctly.

On iOS each sound file must be added to the SDK's Xcode project in order
to be bundled correctly. To playback we need to know the path of the SDK
bundle which is now exposed by the AppInfo iOS module.

This only works automatically on Android >= 8. On other platforms / versions, it
relies on the SDK user on implementing a "reduced UI" mode and reacting to the
"request PIP" delegate method.

Story time.  Currently the app can be started in 4 ways:

- just tapping on the icon
- via a deep link
- via a universal link
- via the phone's recent calls list

The last 3 options will make the app join the specified room upon launch. React
Native's Linking module implements the necessary bits to handle deep or
universal linking, but CallKit is out of its scope.

In order to blend any type of app startup mode, a new LaunchOptions module (iOS
only) exports a getInitialURL function, akin to the one in the Linking module,
but taking CallKit instents into consideration. This function is then used to
make app startup with a URL consistent across all different modes.

Fixes: #2377 #2267 #2158

Due to the difference in nature, the iOS and Android implementations are
completely different:

iOS: MPVolumeView is used, which allows us to place a button which will launch a
native route picker provided by iOS itself. This view is different depending on
the iOS version, with the iOS 11 version being more complete.

Android: A completely custom component is used, which displays a bottom sheet
with the device categories, not devices individually. This is akin to the sheet
in the builtin dialer.

The root view was not adjusting it's bounds after device rotation.

Revert "[RN] Remove unnecessary source code" (commit
a3441030a3). But since the project file
needs to explicitly mention the CallKit and Intents framework, do not
use the semantic @import as that's confusing in the case.

CocoaPods has made some updates to the bundled resource files.

* Javadoc introduced @code as a replacement of <code> and <tt> which is
  better aligned with other javadoc tags such as @link. Use it in the
  Java source code. If we switch to Kotlin, then we'll definitely use
  Markdown.

* There are more uses of @code in the JavaScript source code than <tt>
  so use @code for the sake of consistency. Eventually, I'd rather we
  switch to Markdown because it's easier on my eyes.

* Xcode is plain confused by @code and @link. The Internet says that
  Xcode supports the backquote character to denote the beginning and end
  of a string of characters which should be formatted for display as
  code but it doesn't work for me. <tt> is not rendered at all. So use
  the backquote which is rendered itself. Hopefully, if we switch to
  Markdown, then it'll be common between JavaScript and Objective-C
  source code.

This commit adds initial support for CallKit on supported platforms: iOS >= 10.

Since the call flow in Jitsi Meet is basically making outgoing calls, only
outgoing call support is currently handled via CallKit.

Features:
 - "Green bar" when in a call.
 - Native CallKit view when tapping on the call label on the lock screen.
 - Support for audio muting from the native CallKit view.
 - Support for recent calls (audio-only calls logged as Audio calls, others show
   as Video calls).
 - Call display name is room name.
 - Graceful downgrade on systems without CallKit support.

Limitations:
 - Native CallKit view cannot be shown for audio-only calls (this is a CallKit
   limitaion).
 - The video button in the CallKit view will start a new video call to the same
   room, and terminate the previous one.
 - No support for call hold.

It provides access to the app's display name and version.

Based on work authored by Shuai Li <sli@atlassian.com>, Daniel Ornelas
<dornelas@atlassian.com>, and Lyubo Marinov <lmarinov@atlassian.com>.

The error is stored in the redux store in base/config so other components can
consult it. It is also broadcasted as a new event in the external API for the
SDK.

JitsiMeetViewListener currently has methods of one and the same pattern
so adding new methods i.e. events i.e. redux action types is a question
of repetition in the Java source code. Speed up the support of new
events by trying to deal with them in a generic way.

The same goes for JitsiMeetViewDelegate.

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.

We must not pass nil as the URL, that will translate to null and we won't be
able to load the initial URL which is passed as the launch parameters.

NSDictionary doesn't support nil values, they must be objects, so use NSNull
instead, which is the kosher way to do it.

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.