refactor: `ChatRoomFactory` returns real `ChatRoom`s

- `ChatHomeService` only deals with real `ChatRoom`s.
- Hence, there is no need for `ChatRoomFactory`, to return the simplified
  interface `ChatRoomInfo`.
- This is, because the implementation specific logic is implemented in the
  `ChatHomeService`, not `ChatHome` itself: the actual implementation is
  hidden behind that service (and behind the service `ChatRoomService` in
  the domain-class `ChatRoom`).