The lib will accept new style constraints and use those
to capture audio/video. By defining the constraints in
config, there is greater flexibility for defining
and changing constraints.

* Javadoc introduced @code as a replacement of <code> and <tt> which is
  better aligned with other javadoc tags such as @link. Use it in the
  Java source code. If we switch to Kotlin, then we'll definitely use
  Markdown.

* There are more uses of @code in the JavaScript source code than <tt>
  so use @code for the sake of consistency. Eventually, I'd rather we
  switch to Markdown because it's easier on my eyes.

* Xcode is plain confused by @code and @link. The Internet says that
  Xcode supports the backquote character to denote the beginning and end
  of a string of characters which should be formatted for display as
  code but it doesn't work for me. <tt> is not rendered at all. So use
  the backquote which is rendered itself. Hopefully, if we switch to
  Markdown, then it'll be common between JavaScript and Objective-C
  source code.

The name better suits its purpose, since it can be called at any time.

* 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

Because on web video track is stored both in redux and in 'localVideo'
field, video is attempted to be unmuted twice when turning off the audio
only mode. This will crash the app with 'unmute operation is already in
progress'. This commit will prevent from taking action from the web
world if the video track already exists and will make the redux side
rollback unmuted status in case unmute fails.

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.