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.
Great point!  It's defined at the top of the page, along with User, and Post.  This'll hopefully make the actual code content shorter to write.