Fixed up de-duplication issues

This finishes up the de-duplication of adding users to a conversation as well as adding a conversation to a user's conversation list.  It should also restore functionality to many things that are currently broken on master.

Conversation.js is getting a bit messy and bloated, perhaps a refactoring should be considered in a future PR.
I think it'd be good to clarify what action we pursue after this check. 'Check that we aren't pushing in a duplicate conversation. If we are, then...'