Level Editor Undo/Redo

Here is a undo/redo system based on this. Added the regular Ctrl+z for undo and Ctrl+y for redo.
It supports undo/redo for:
Tell me what you think.
It supports undo/redo for:
- Adding and Removing objects
- Moving objects
- Adding and Removing paths
- Adding and Removing links
Tell me what you think.