- Re-use the native redux pinning implementation for web
- Remove pinning logic from conference.js
- To the native pinning add a check for sharedVideo so
  youtube videos do not send a pin event
- Add shared videos as a participant to enable pinning and
  so they can eventually get added to the filmstrip
- Emit UIEvents.PINNED_ENDPOINT from middleware

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.