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'd say that we can probably delete this final line at the end of the method description and just close comments after the last line with text (in this case, 'participant.').