Prepare for React 16.

* feat(local-video): convert to react

- Create a VideoTrack component for displaying a video element.
  This mirrors native also having a VideoTrack component.
- The VideoTrack component does not let React update it to prevent
  the video element from re-rendering, which could cause flickers
  and would not work with temasys's overriding of the video element.
- VideoTrack extends AbstractVideoTrack to mirror native
  implementation and to get the dispatch of the onplaying event.
- Remove the onclick handler on the video element. Honestly, I
  didn't get it to work, and did not try, but it is also unnecessary
  because another handler already exists on the video wrapper.

* ref(device-selection): VideoInputPreview uses VideoTrack to show video

* squash into conversion: change css selectors

* squash into conversion: mix in abstract props

* squash into conversion: change shouldComponentUpdate check

* squash: update comment about why triggerOnPlayingUpdate is used

Introduce certain React Components which may be used to write
cross-platform source code such as Audio like Web's audio, Container
like Web's div, Text like Web's p, etc.

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.