Allow per-room config

[guusdk]

Configuration is now applied globally, to all rooms. We can (and should) allow room-specific configuration. That, for instance, would allow us to have one room that's audio-only, while we have another room where the default video resolution is higher than default.

[deleolajide]

Probably not the right place to discuss this, but definitely related to this is to give muc rooms their own user-defined properties like users, groups and bookmarks have. It would serve this purpose