We deal with Escape and Cmd+. manually in a lot of places in Qt. We should add a QKeySequence for them, which would also make it possible to trap the cancel action in QML when non-native windows are used for dialogs.

See also:

https://developer.apple.com/library/mac/documentation/Cocoa/Reference/ApplicationKit/Classes/NSResponder_Class/#//apple_ref/occ/instm/NSResponder/cancelOperation:

`QMessageBox::keyPressEvent`