UndoMenuItem can be subclassed to implement custom texts for undo and redo functions

The class has one event, UpdateMenuText which will be called with the new text, state and the
control whos state change will be undone/redone.

Return true from the event if you've handled setting the text and state.

To use a subclass, pass an instance/instances to TheBigUndo.AddUndoMenuToMenuBar