Revert method missing

[swayhead]

It would be nice to have a "cancel/revert/restore" method to re-establish the state prior to dragging. Could be useful inside callback functions.

[skylord123]

I would like to reference #90 for people trying to accomplish this without a current solution.

[lukasoppermann]

Basically to make this work we would need to:

• [ ] store some kind of history of the most recent changes (this could be done using browser local storage)
• [ ] add a revert function that when triggered restores to the latest version and updates the local storage