Adds ConferenceDescription and ConferenceDescriptionPacketExtension classes.
Adds a publishConference(ConferenceDescription) method to the ChatRoom
interface.
Implements ChatRoom#announceConference for jabber. It works by sending a
ConferenceAnnouncementPacketExtension in a Presense packet to the MUC.
Makes ChatRoomJabberImpl monitor incoming Presense packets for such extensions.