- Instead of having 4 listeners for local connection status
  updates and 1 for remote, remove two of the redundant listeners.
- Instead of calling into 4 separate VideoLayout methods to update a
  participant's connection status, expose one handler.

* ref(video-layout): move middleware for TRACK_ADDED

* ref(video-layout): call mucJoined when redux knowns of conference join

Instead of keeping dominant speaker locally, get it from redux and be
updated when the dominant speaker changes. This is in an attempt to mimic
the video layout being reactified and connected to redux.

The goal will be to make video layout stateless and instead
get all state from redux.