This has a number of failings currently: 1) It needs to hide the 1:1 conference
room, 2) Swapping tabs on the outbound call mutes audio (this just seems to be
a vector bug since I can repro this on a normal 1:1 voip call), 3) Needs a big
plinth/etc to say the conf call is in progress.
CallView is the container for either VideoViews or WaveformViews. All UI
elements listen for 'call_state' payloads and then call
CallHandler.getCall(roomId) to extract the current MatrixCall for that room.
We can't do this via stateful dispatches because dispatching does not preserve
ordering empirically (probably due to setTimeout).
