Adds two new messages which clear the users emoji statuses. This messages
enables this task to be done in a single call, instead of triggering one
method call for each user.
'ClearAllUsersEmojiCmdMsg' is sent from meteor to akka and updates all the
emoji states in the users model.
'ClearedAllUsersEmojiEvtMsg' is sent from akka to meteor. This triggers the
mongo collection update.
