Now that Apple have approved build 1.2.199 for release in the App Store,
the short app version needs to be incremented; otherwise, no new builds
can be uploaded to TestFlight and, respectively, for release in the App
Store.

Turns out React Native's timers (setTimeout / setInterval) don't run while the
app is in the background: https://github.com/facebook/react-native/issues/167

This patch replaces the global timer functions with those from the
react-native-background-timer package, which work in the background.

These timers won't magically make an application work in the background, but
they will run if an application already happens to run in the background. That's
our case while in a conference, so these timers will run, allowing XMPP pings to
be sent and the conference to stay up as long as the user desires.

The implementation varies across platforms, with the same goal: allow the app to
use the entire screen real state while in a conference.

On Android we use immersive mode, which  will hide the status and navigation bars.

https://developer.android.com/training/system-ui/immersive.html

On iOS the status bar is hidden, with a slide effect.

- Maximum of 80 characters per line.
- Group first and then sort in alphabetical order.
- Fields should begin with a lowercase letter.

This module chooses the most appropriate audio default based on the specified
mode.

Use a minimum SDK version of 19, that is Anroid 4.4 (KitKat) and a target SDK of
23, that is, Android 6.0 (Marshmallow).

Now that Apple have approved build 1.1.185 for release in the App Store,
the short app version needs to be incremented; otherwise, no new builds
can be uploaded to TestFlight and, respectively, for release in the App
Store.

Now that Apple have approved build 1.0.178 for release in the App Store,
the short app version needs to be incremented; otherwise, no new builds
can be uploaded to TestFlight and, respectively, for release in the App
Store.

The variables in gradle.properties can be overridden on command line like: -Pversion=1.

Bundle our custom icon font jitsi.ttf in the Android app (which we
already do for the iOS app).

Additionally, remove icon font files which are not in use.

As a step toward merging jitsi-meet-react with jitsi-meet to share as
much source code as possible between mobile and Web, merge the part of
jitsi-meet-react's source tree which supports mobile inside the
jitsi-meet source tree and leave jitsi-meet-react's Web support in the
source code revision history but don't have it in master anymore because
it's different from jitsi-meet's Web support. In other words, the two
projects are mechanically merged at the file level and don't really
share source code between mobile and Web.