* Closes https://github.com/emilk/egui/issues/1713
I almost went to implement my own undo/redo system, and then found the
egui undoer.
Went to make a small demo to test for myself how it worked, and then
found the linked issue.
So here is a tweaked version of that :)
Co-authored-by: Wybe Westra <w.westra@kwantcontrols.nl>