Bug fixing

Bug fixing mostly this time:

Undo/Redo seems to be fixed completely in all known cases to have problems.
- there was a case when undo (or redo) crashes silently when it need to remove objects
- undo was used not properly in case of extrude and let some objects floating

I was looked with bxtrx initially for leaks and found a part of the problem (as it was related with OCC and not with TreeView and PropertyView).

Right now I'm investigating why propagating events in cascade happen to generate to many times in case of a chained extrude list and gets even recursively. I did not found yet the reason because it blocks easily. With the leak fixed the solving hopefully will be much more smoother.