Undo manager prevents entering Alt + Z special characters

Hey guys,

we were just reported that some of our users can't enter special chars like ż, Ż (alt + z). That event.metaKey in undo / redo commands messes it up. Can't think of any good way to fix this, so I'm not creating a pull request.

In our case - we just stopped using undo / redo by removing the key bindings, but it would be great to be able to use those while not loosing those special Z chars.