fix: GREEN - Implemented activation/deactivation of `ChatRoomData`

fix: GREEN - Implemented activation/deactivation of `ChatRoomData`

* Introduced `volatile ChatRoomData#active`, which initially is `false`.
* `ChatRoomData#listen()` throws `ChatRoomInactiveException` if inactive.
* `ChatRoomData#addMessage(..)` throws `ChatRoomInactiveException` if
  inactive.
* `SimpleChatHomeService` explicitly activates restored and newly created
  instances of `ChatRoomData`.
* `DataChannel` explicitly activates instances of `ChatRoomData`, if
  they are restored during partition-assignment or, if a new chat-room
  is created.
* `DataChannel` explicitly _deactivates_ instances of `ChatRoomData`,
  if the associated partition is revoked.
* Also: Introduced `ChatMessageService#getChatRoomId()`.