- Adds the ability to share video as a "PiP" when screenshare is in progress.
- Add a method for creating a local presenter track.
- Make sure isLocalVideoTrackMuted returns the correct mute state when only screenshare is present.
- Make sure we get the updated window size of the window being shared before painting it on the canvas.
- Make sure we check if the shared window has been resized

Simplify the code by using a bitfied instead of a couple of boolean flags. This
allows us to mute the video from multiple places and only make the unmute
effective once they have all unmuted.

Alas, this cannot be applied to the web without a massive refactor, because it
uses the track muted state as the source of truth instead of the media state.

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.