Currently just by adding /holdcall and /unholdcall slash commands
The only place the hold status of the call is currently represented
is when the call is a voice call and you're viewing a different room:
it's not wired up when you're viewing the room because that currently
uses the room status bar which it won't do with the new UI.
Also convert VideoFeed to typescript, and remove videoview because
it essentially just managed the fullscreen functionality, but we'll
want and 'on hold' representation (and probably chrome for hagnup etc)
in the fullscreen UI too, so let's just make CallView the thing that
gets fullscreened.
* Remove the two separate enumerations of call state: now everything
uses the js-sdk version of call state. Stop adding a separate
'call_state' field onto the call object(!)
* Better reflection of the actual state of the call in the call bar,
so when it's connecting, it says connecting, and only says 'active call'
when the call is actually active.
* More typey goodness
and remove the old conference call stuff while we're at it: enough
time should have passed since those mistakes that we can move on.
The old conference call rooms will still appear for anyone whose
account dates back to that time, but they've presumably been appearing
in any other matrix client they used too.
