Add basic drag 'n' drop support for adding applets to a Corona.
The idea is that when the label from the ControlBox is dragged onto a Corona, a real applet is created which should then be moved around until the mouse is released.It currently doesn't place the applet anywhere contextually since the dragLeaveEvent(), dragMoveEvent() and dropEvent() event functions are not called for some reason.

If anyone knows, please tell :) Maybe we will have to subclass QGraphicsScene in order to catch the events there?