In order to obey a palette set globally on QApplication, an application
attribute for checking if it's set at all is added.
Task-number: QTBUG-39800
Change-Id: I26b965e6e18e0e1ca4df03cf343b3527df3636b2
Reviewed-by: J-P Nurmi <jpnurmi@theqtcompany.com>
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@theqtcompany.com>