When we enter the overview, we don't explicitly don't take a grab, so we
shouldn't connect to key-focus-changed and things like that, otherwise
random overview code will drop our grab for us.
This fixes escape in the overview not dropping when a notification is up.
Make sure to account for modalCount properly, rather than just
tracking modalCount for the last actor on the stack. Additionally,
traverse the popped actors in the reverse order so that onUngrabbed
callbacks are called at the proper place in time.
