Finishing implementing file rename/move

[williamstein]

Right now renaming or moving a file in the UI simply does the corresponding operation on the underlying filesystem. It doesn't do anything else at all (since we simply didn't implement anything else yet!).

• Send a message to the local hub to update the sync object
• Send a broadcast message out to all attached global hubs and connected clients that the path/filename changed
• What else?

(reported by Christophe Bal, among others)