Add shutdown hook to cause disconnect from device when user quits the app

[GoogleCodeExporter]

Currently, the app only disconnects from the bot if you click the close button 
on the window.  If you quit using the keystroke command (command-Q on a Mac) or 
quit from the menu bar (Mac), then the app is just stopped and the bot is never 
told about the disconnect (leaving it to discover it on their own and 
eventually time out and revert to song mode).

Original issue reported on code.google.com by garthabr...@gmail.com on 13 Jul 2011 at 9:41