refactoring of MucRoom to support multiple client connections per nickname
Merge branch 'master' of github.com:Kixeye/kixmpp

Conflicts:
	kixmpp-server/src/main/java/com/kixeye/kixmpp/server/cluster/task/RoomBroadcastTask.java
	kixmpp-server/src/main/java/com/kixeye/kixmpp/server/module/muc/MucRoom.java