Qt Designer: Implement property() for QAxWidgetPropertySheet.

Access the control property of the QAxWidget directly.

Task-number: QTBUG-34592

Change-Id: I7d0971ad8fc265d0443da7ae72330e2b7f3a8d70
Reviewed-by: Oliver Wolff <oliver.wolff@digia.com>
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>