Added migration support for spells — The Labyrinth Steam update #655461

There's not much on the user-end of this update, but the one thing I added will allow all future updates to be a lot smoother for you guys! I added migration support for spells. That way if I change the way a spell works, change its values, or otherwise rework it in some way, your old saves with old functionality will be able to migrate to the new functionality! Before this update, spells would overwrite any new changes I made to a spell in an update. This is frustrating on old saves since it means you aren't guaranteed to have new functionality as I rework and change spells. But now spells have a backbone for migrating over to new updates, allowing them to update and inherit any new changes, giving old saved spells the capability to update to new versions. This will cut down on the amount of times you have to restart the game since significant changes to spells would often mean old save...