plugin XEP-0045, quick frontend (app,chat): various chat improvments: - (XEP-0045): join defered is now fired when room is full joined and history is available - (XEP-0045): mucJOIN signature has changed, it now returns the same arguments as mucRoomJoined and a boolean which is True if the room was alread joined - quick frontend (app, chat): adapted code to new changes