Adds a new action labelling the starting point of a saved state

[NicoKiaru]

If one loads a saved state and perform some actions, it's very hard to know when to stop canceling in order to restart from the saved state.

It would be nice to add an action which serves as a label for this starting point. When the user wants to cancel it, it would just display a message in the GUI (and be silent in headless mode, or print in the default system output).