title: Qt: having selected items appear on top in QGraphicsScene
body: <p>So i have a <code>QGraphicsScene</code> with various items. Some of the can take the same coordinates  in the scene. When I display the scene the ones displayed on top are the ones which were added last. Is there a way to make a certain item always appear on top or even better make it reappear on top during the program (rather than deleting it and adding it again)?. I've been thinking about drawing everything beforehand and then using <code>setVisible()</code> to show only the items I want to, but since I want to add new things online it seems to be a bit problematic.</p>