Big refactoring.

Removed ControlBox model, and instead only create ChatBox models inside
ChatBoxes collection (the Controlbox is now also a ChatBox).

This enables us to use backbone.localStorage for saving open chatboxes (saving
and fetching currently not implemented).

createChatBox now doesn't return a ChatBoxView instance anymore. In the case
where a view was needed (to append a message), we create the message on the
ChatBox and let the view update via an event trigger. This is much more Backbonic ;)

Also created a Message model. This will most likely enable us to in the future also
store messages via backbone.localStorage.