Bug 1104003 - [Loop][Rooms] Create basic 'room' screen

See bug https://bugzilla.mozilla.org/show_bug.cgi?id=1104003 please. Action happens at https://github.com/jaoo/firefoxos-loop-client/tree/1104003.
Move `action` and `clientMaxSize` to const, and `displayName` must be `Controller.identity`