Refactored RosterAddedMessage/RosterDeletedMessage into one
RosterMessage. 
Added code to finalizeRegistration to send a message to all other
participants when a user joins a chat.
Added code to finalizeDetach to send a message to all other participants
when a user is removed from a conversation.
Added code to the NameCheckController to sanitize name input.
Added code to the SockJsHandler to remove a user when session closes.
Removed PresenceMessage.
Merge pull request #16 from ualerts-org/notifyParticipantsOfAttendance_ACE-46

Refactored RosterAddedMessage/RosterDeletedMessage into one