Bug fixing on document/tree data

I was looking to solve all bugs related with loading/undo-redo cycle. There is only onle harder bug in this category and I hope to find why is happening (the situation that an undo step will override some values out of the undo changes, the worst of this bug is not to find what was doing it, but I think at least in future, the fix should enforce that an undo operation to not change anything that Undo step states). For now I've fixed a bug that deleting a shape was not removed internally, but was just hidden from the user eye point of view, which breaks the face splitter. Based on design, the face spliiter being a part of the tree, on the actual code, was removed too at some specific operations (like save/open). Right now Face Splitter and some other future shapes that may need to not be deleted if they are invisible (like constraints!?), they may get by design this extra attribute and to not break the delete code.