#13 exit confirmation issues

[frankie]

* The application level exit confirmation prompt appears regardless of whether there are unsaved changes.
* An edited scene has its own exit confirmation prompt if there are unsaved changes
* Its possible for both of these to appear at the same time
* if the scene exit confirmation prompt is visible, and you choose confirm quit on the application level exit confirmation prompt, it doesn't actually exit the application

[frankie]

have removed the application level exit confirmation.

I think the scene/library level confirmations need an additional cancel option which will abort the exit process