* QShortcut falls down on duplicates. It can have activatedAmbiguously
events, but these happen in arbitrary order and the shortcuts on
menu items just swallow the ambiguous activate so it's not useful.
* Instead we just let MainWindow pick up ShortcutOverride events and
consult a mapping of which shortcuts to use. We can use a smarter
selection method to choose the more 'local' shortcut if two shortcuts
that conflict exist.