Correct event handlers to trigger in all instnces

Some events don't propagate correctly to the right sub-window
and some things like the pad handler don't even necessarily have
windows. So, just register some events with the top-level app.

Also add a virtual destructor to the PadHandlerBase to be able to
deal with multiple inheritance in the derived classes.
Merge pull request #1 from Bigpet/guiEvents

Correct event handlers to trigger in all instances