- Create new React Components for RemoteVideoMenu and its
  buttons
- Remove existing menu creation from RemoteVideo
- Refactor RemoteVideo so all function binding happens once in
  the constructor, removing the need to rebind when updating
  the RemoteVideoMenu
- Allow popover to append and remove React Components from itself
- Refactor popover so post-popover creation calls are broken out and
  popover removal behavior is all done in one function.

When callstats is not configured hide the button.

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.