* ref: video muted state

Get rid of 'videoMuted' flag in conference.js

* ref: audio muted state

Get rid of 'audioMuted' flag in conference.js

* fix(conference.js|API): early audio/video muted updates

* ref(conference.js): rename isVideoMuted

Rename isVideoMuted to isLocalVideoMuted to be consistent with
isLocalAudioMuted.

* doc|style(conference.js): comments and space after if

* ref: move 'setTrackMuted' to functions

* fix(tracks/middleware): no-lonely-if

* ref(features/toolbox): get rid of last argument

* ref(defaultToolbarButtons): rename var

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.

Listeners were set for when a track muted or changed its video
type, but the listeners were never removed. This would could
cause events to keep firing on the removed tracks, which would
cause redux to fire and error because the tracks were no longer
known. That the tracks still fire events after removal is
another issue...

- Add tracks to the redux store by intercepting where the
  tracks actually get used via conference.replaceTrack
- While the replace call is unique to web, the _dispose and
 _addTracks calls use existing native code implementations
- Between _dispose and addTracks is a call to update mute state.
  Without it, when changing devices or videoType while muted,
  the user will stay muted (whereas existing web behavior
  causes unmute). This is due to middelware calling
  _syncTrackMutedState to make the track mute if the user is
  currently muted.
- Move the rest of ConferenceEvents.TRACK_MUTE_CHANGED into
  middleware so the event is no longer used
- Note: This change does not guarantee the track state in the
  redux store will be 100% accurate, specifically the attribute
  videoStarted. Muted and videoType should be accurate.

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

Lib-jitsi-meet does not really implement isScreenSharing. Besides,
getCameraFacingMode will already make sure that the video track does not
represent a desktop stream.

Until we make a decision on access modifier hints and adopt a respective
coding style, consistency is king.

An error was discovered and fixed by GitHub user blackneck in
jitsi/jitsi-meet PR #1017. The faulty source code was a piece of
duplication though. Remove the source code duplication there to reduce
the risks of bugs.

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.