Add properties sheet to the diagram

[vainolo]

Add properties sheet to the diagram

[vainolo]

Finished implementation. Had to do some looping around because the GEF implementation of an undoable property sheet does not work with EMF provided items, so after lots and lots of reading the elegant solution I found was to let the OPMGraphicalEditor create a property sheet using the getAdapter mechanism (to make things generic), then I had to re-implement some classes like the PropertySheetProvider - to change the source of the properties for an editPart (use the model not the editpart as source), and also had to wrap the propertysources that EMF returns so that they worked correctly with GEF. I don't know if my solution will work in every case but seems OK and I think it is more elegant than other solutions I read on the net.