Allow a "Rapid Rollback" to rollback many steps at once.

[dcorbin]

Sometimes, when the game is over, we'd like to replay it from a certain point if a different action has been taken. In a completed game, allow "Rollback to the current turn" in the Rewind view. As an option, allow it as a change to the current game, or making a new game that is started in the current state, but with the cards in the deck re-randomized.