Translate Super/Hyper keys to MetaModifier

This is how it was done in Qt4. If users are interested
in an actual X11 keysym they can use QKeyEvent::nativeVirtualKey().

Change-Id: I710664e48c5db1633a357aa0a5d238f3453103ab
Task-number: QTBUG-38428
Reviewed-by: Christian Stenger <christian.stenger@digia.com>
Reviewed-by: Lars Knoll <lars.knoll@digia.com>
Reviewed-by: Sebastian Kügler <sebas@kde.org>
Reviewed-by: Shawn Rutledge <shawn.rutledge@digia.com>