Android uses a SurfaceView to render video, which is not quite a View, so the
fade-in animation (which varies the opacity) doesn't work.

Instead, add an opaque black view covering the video, which transitions to
transparent. This creates much smoother transitions on Android, while behaving
the same.

In addition, I removed the flip animation for local tracks, which is no longer
used, since the camera is switched without changing tracks.

The files styles.js are used (pretty much) on React Native only and each
of them exports 1 name. Export it as default to cut down on source code.

It's now natively supported:
https://github.com/oney/react-native-webrtc/pull/244

As an intermediate step on the path to merging jitsi-meet and
jitsi-meet-react, import the whole source code of jitsi-meet-react as it
stands at
2f23d98424
i.e. the lastest master at the time of this import. No modifications are
applied to the imported source code in order to preserve a complete
snapshot of it in the repository of jitsi-meet and, thus, facilitate
comparison later on. Consequently, the source code of jitsi-meet and/or
jitsi-meet-react may not work. For example, jitsi-meet's jshint may be
unable to parse jitsi-meet-react's source code.