I can undo an editing mistake immediately

(User Story, To be Fixed , Priority: High, Test Status: No automated tests yet , Reported By Justin du Coeur, )
User Interface
Summary: When I am viewing / editing a Thing, I can say Ctrl-Z to undo changes, as usual for Windows.
This is plausible due to the new client. We can hook all edit controls, and intercept all changes. We build these into a Change Stack, and provide a way to undo changes, one at a time.
This is not the sort of full-scale long-term Undo I want to get to, do it's a fairly easy short-term improvement to the situation.