Introduce navigation for all in-conference screens.

feat(external_api) exposes more events from JS to native and adds the ability to send actions from native to JS.

Looks like the "Firebase Analytics" dependency is needed when migrating to the
new Firebase Crashlytics SDK. We are only interested in the "latest iversion
crash-free users" stat, which seems to require this. The documentartion is
somewhat confusing though.

JSC wasn't the cause for the crash we were hunting after all. RN doesn't set
HErmes as the default, neither does Expo, so the jury is still out on Hermes,
and it looks like JSC is still the safest bet.

In addition, the way Hermes is packaged (as a standalone AARs, instead of a
local "Maven repo") complicates the SDK build and can make the resulting build
bloated.

Android < 23 is currently less than 3% for us so let's try to lower the
maintenance burden. Users can still download an older version no problem.

When exiting PiP with by pressing the X the onPictureInPictureModeChanged method
is called. Since onResume is called a while after, in case the maximize button
is called, it's not easy to know if the user pressed the X button, and that was
the cause for exiting PiP.

So, in order to avoid show the user they are still in the meeting, bring the
activity to the foregound so they can hangup.

Android for Enterprise provides special feature for applications to obtain configuration through RestrictionManager remotely by some MDM solution.

Jitsi Meet can be remotely installed and provisioned with a proper URL (making URL not editable by the user) inside the Work Profile or Fully managed device.

It's the source of uncountable problems for which we don't have a good
solution, since they are caused by buggy implementations of self-managed
connection services by manufacturers.

It's not necessary and makes the build faster.

Fixes running profile builds.

The notification is posted by a foreground service, which also has the nice
side-effect of keeping the app alive for a long time.

It may be called in the Activity instead of in the Fragment. Handle both.

At the moment it includes:

- display name
- email
- avatar URL

This information is used *only* if no token was specified.

A libre build will exclude the following:

- Analytics modules
- Google Play services GMS
- Crashlytics
- Firebase

It's a number whichb must be ever increasing with each build submitted to the
store.

Automate its value by using the number of seconds since 1st of January 2019.
That should be enough for ~680 years.

When running the app from Android Studio the React packager is not automatically
started. In vanilla RN projects this is done by the "react-native run-android"
command, but often times it is desired to run from Android Studio.

This fixes that by starting the packager from Gradle.

Consolidate all failure cases into a single one: CONFERENCE_TERMINATED. If the
conference ended gracefully no error indicator will be present, otherwise there
will be.

It renders a single JitsiMeetFragment which holds the JitsiMeetView view.

Co-authored-by: Saúl Ibarra Corretgé <saghul@jitsi.org>

Add JitsiMeetFragment and refactor the app to use it.