Includes some refactoring:

- Don't send an `active` chat state notification when entering a MUC
  I can't think of a good reason why this might be necessary or desired.
- Move `setChatState` form the view to the model
- Remove unused method `handleChatStateNotification`
- Don't store `role` and `affiliation` for the current user on the
  ChatRoom object, but instead on the ChatRoomOccupant object representing
  the user.