Co-authored-by: DimaG <dgeorgiev06@gmail.com>

Provide a default and builtin default implementation which finishes the
Activity, same as before.

What this PR removes is the ability to provide a custom default handler because
applications can already take this decision when calling `onBackPressed`. In
addition, make `onBackPressed` return `void` because it's virtually impossible
for it to return `false` (that would mean that there is no
`ReactInstanceManager`, which means there is no app to begin with).

In addition, remove the use of `BackAndroid` since `BackHandler` contains an iOS
shim now.

* feat(tile-view): initial implementation for mobile

- Create a tile view component for displaying thumbnails in a
  two-dimensional grid.
- Update the existing TileViewButton so it shows a label in the
  overflow menu.
- Modify conference so it can display TileView while hiding
  Filmstrip.
- Modify Thumbnail so its width/height can be set and to prevent
  pinning while in tile view mode.

* use style array for thumbnail styles

* change ternary to math.min for expressiveness

* use dimensiondetector

* pass explicit disableTint prop

* use makeAspectRatioAware instead of aspectRatio prop

* update docs

* fix docs again (fix laziest copy/paste job I've ever done)

* large-video: rename onPress prop to onClick

* change forEach to for...of

* use truthy check fallthrough logic instead of explicit if

* put tile view button second to last in menu

* move spacer to a constant

* the magical incantation to make flow shut up

Moves NotificationContainer to the toolbox and filmstrip container, so
that there's no need to manually calculate the positions.

Unfortunately, as the Jitsi Meet development evolved the routing mechanism
became more complex and thre logic ended up spread across multiple parts of the
codebase, which made it hard to follow and extend.

This change aims to fix that by rewriting the routing logic and centralizing it
in (pretty much) a single place, with no implicit inter-dependencies.

In order to arrive there, however, some extra changes were needed, which were
not caught early enough and are thus part of this change:

- JitsiMeetJS initialization is now synchronous: there is nothing async about
  it, and the only async requirement (Temasys support) was lifted. See [0].
- WebRTC support can be detected early: building on top of the above, WebRTC
  support can now be detected immediately, so take advantage of this to simplify
  how we handle unsupported browsers. See [0].

The new router takes decissions based on the Redux state at the time of
invocation. A route can be represented by either a component or a URl reference,
with the latter taking precedence. On mobile, obviously, there is no concept of
URL reference so routing is based solely on components.

[0]: https://github.com/jitsi/lib-jitsi-meet/pull/779

The visibility of the toolbar can be toggled by interacting with the main screen.
This change allows the toolbar to be configured to be 'always visible'. This voids
the 'toggle' functionality.

As part of the work on fixing the problem with the multiplying
thumbnails, we've associated remote participant w/ JitsiConference.
However, there are periods of time when multiple JitsiConferences are in
the redux state (and that period is going to be shorted by
StateListenerRegistry). In order to give more control to the feature
base/participants, reduce the occurrences of direct access to the
features/base/participants redux state and utilize the feature's
existing read access functions. Which will allow us in the future to
enhance these functions to access participants which are relevant to the
current conference of interest to the user only.

Show it if we are the only participant, and hide it the moment someone else
joins the conference.

Since the main conference container is no longer "clickable" there must
be a way for clicking on the "large video". A clickable TestHint nested
in ParticipantView makes it easier for dealing with the fact that the
click handler is not always on the same component (required for the
pinch and zoom feature to work correctly).

Be explciit about the appearance we desire, since each mounted StaturBar
component will override the existing values. In this case, the problem was
caused because the default on iOS is dark, whereas it's light on Android.

Set it to light so it works consistently across both, which is what we want.

Adds TestConnectionInfo component which exposes some internal app state
to the jitsi-meet-torture through the UI accessibility layer. This
component will render only if config.testing.testMode is set to true.

TouchableWithoutFeedback and TouchableHighlight interfere with the
implementation of 'pinch to zoom' to come. We prepare for it by driving
the onClick/onPress handler(s) out of Conference, through LargeVideo and
ParticipantView into Video itself where the bulk of 'pinch to zoom' will
be implemented.

In preparation for "pinch to zoom" support in desktop streams on mobile, make
certain Views not intervene in touch event handling. While the modification is
necessary for "pinch to zoom" which is coming later, it really makes sense for
the modified Views to not be involved in touching because they're used to aid
layout and/or animations and are to behave to the user as if they're not there.

It's designed to cover a container and give it a "tint" by using a color and
opacity.

It's not supposed to go on top of everything, like an error would. It's tied to
a conference, so render it outside of the OverlayContainer.

On web Conference is pretty much all there is, but on mobile we have the welcome
page and the blank page. If we fail to load config.js, for example we will still
be in the welcome page *and* we want to show an error overlay.