title: qt drag and drop in qgraphicsScene
body: <p>I have 2 custom qgraphicsitems on a qgraphicsScene, rendered by a qgraphicsview. Now I want to be able to drag and drop one of the 2 items to the other kind. But which events should I reimplement for this? The documentation is a bit confusing on this.</p>
  
  <p>also I want the qgraphicsitem to jump back to its original position if the user drags it to another area than the qgraphicsitem it should be dropped on.</p>