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).
* sans-serif font
* use display: table for the message list so that everything lines up nicely
* switch to flexbox layout rather than position absolutes to avoid assuming a full screen UI and improve maintainability (and better match atomify)
* neutralise the colouring and styling of highlighted rooms in the recents list
* switch from ul + li's to a series of divs in some places where the li's are achieving nothing but adding more complexity to the DOM
* add mx_MessageTileType as a generic css base class for all message tiles
