Rewrite call state machine
* 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
