Use the curstom _switchCamera API provided by react-native-webrtc to toggle the
camera instead of destroying the current track and creating a new one.

_switchCamera is implemented at a low level, so the track perceives no changes,
thus being a lot faster and less involved since the capturer doesn't need to be
destroyed and re-created.

In addition, don't mirror the video for the back camera.

Ref: https://github.com/oney/react-native-webrtc/pull/235

When a new local video track is created an associated video capturer is created
for it. The cause for the freezes seems to be creating mutliple tracks (which
come with a video capturer each). Fix this by first disposing of the previous
video track before creating the new one.

Ref:
https://github.com/oney/react-native-webrtc/issues/209#issuecomment-281482869

Redux actions which represent "commands" should be imperative, and those
representing events should use the past tense.

The toolbar's mute buttons depict respective features/base/media states.
However, (un)muting is practically carried out by features/base/tracks.
When the mobile app enters a conference configured to invite the joining
participant to mute themselves, the tracks would be muted but the
toolbar's mute buttons would not reflect that.

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.