Test Undo Redo, make sure it actually works at least kind of.

[nicholasammann]

• Update commands to reflect functionality being moved from the MainWindow to the YTELevelEditor workspace.
• Test to make sure the changes didn't break it more than it maybe already is.

[playmer]

I haven't tested this, but I believe it's done. Going to repurpose the issue for testing Undo Redo.