Add information about which action triggered the undo/redo

[marciogurka]

Forum post

"Hello, we are using Gantt and we enabled STM, and we are listening:
restoringstop event to intercept restore events
recordingstop event to handle if the user can undo/redo

Nevertheless, we have two different issues here:

In the restoringstop event I'd like to know if the undo/redo event was triggered by the keyboard or was triggered by a button function (calling the undo(), redo() directly) functions on stm."