Ported class UMLScene and UMLView to QGraphicsScene and QGraphivsView.

This was possible because of the reduced soc2008 and trunk difference approach
performed in the last months by Andy Fischer an me.

The gsoc 2008 branch still contains several fixes and enhancements which may be merged
from now on.

Qt4 related fixes (the most important):
- Usage of QGraphicsItem based event handling
- Usage of QGraphicsScene based rubberband
- Usage of QGraphicsScene/View based item selection

Qt4 unrelated (most important):
- The QPainter based AssocationLine refactoring, which is required for spline based
line style and auto layouts.
- AssociationSpaceManager class for optimized association line drawings.
- The TextItem/TextItemGroup classes, which refactores widgets content setup
- Widget Color gradients, which are useful enhancements of the widget style engine