Add support for QImageIOHandler::Size option in DDS handler.

Change-Id: I7c9fc452142d9827269ebf9b6b2778c2b0eb55da
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>
Fix writing images in DDS handler

Change-Id: If433528eb4cfa7448f171e083dd2bb559dbc2f4a
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>