Getting event when origin has changed.
Entity and waypoint locations update when origin is changed.

However, the origin change now cannot be undone.  Creation of entities
can still be undone.
Add toString().
Works for changing origin, but undoing is broken.
No need to listen to anything here.
Undo works generally, but undoing the origin to (0,0) does not set all
the waypoints to being referenced to (0,0).  No worse than that was.