`Revert` path change

[asinghvi17]

Revert(time, path, n_changes, mode in (:combined, :separate))
Revert(time, changes_to_revert, original_state, mode)

Revert changes along a path. This would be pretty useful if you want to zoom in and then out, but don't want to explicitly write down how much you're zooming.

This would require each change to have a (path-aware) Base.inv(path, change) to create an inverse change.