Normal Editor: History Control
The History Control allows the user to undo and redo Editor events. The control is a list of events previously taken. The current selected event in the list is
the user position in history. The first item in the History Control is always the state of the normal map when it was imported into the editor. There is a limited number of
history events allowed (because of memory). The default is 20 events but this can be changed in the ShaderMap Options and Settings.