Continue working on Undo-Redo cycle

Cris pointed out a problem that some faces remain not deleted still, even I thought that was fixed. The cause was that the removal of shapes is done automatically by NaroCAD as long as there is no consistency breakup. It happen that FaceSplitter keeps references to face shapes and their deletion was erroneous (they remains hidden but leaky) so right now is fixed. I look along for other associated issues.