Move QIcon metatype handlers back to QtGui

Move QIcon metatype handlers back to QtGui

QIcon has been moved back from QWidget to QtGui, so the QIcon QVariant
and QMetaType handler can now be moved back to QtGui.
Also we can give back QIcon its old number, allowing to get rid of some
compatibility hack when unstreaming QVariant

Change-Id: I439d5c2987c06ecd619f394407850f678164afb8
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>
Reviewed-by: Jędrzej Nowacki <jedrzej.nowacki@nokia.com>