Improving the editor's behavior.

This should address issue #1. In summary, when a document changes on the server, the editor will...

 - do nothing if the changes were initiated by the current user
 - do nothing of the changed text and the text in the editor match exactly
 - silently update the text in the editor if the undo stack is empty
 - prompt the user, letting them know there is a newer version available if they'd like to load it.