Reverted DerFlash's last commit. (https://github.com/Mtihc/TreasureChest/commit/32908859b5f978774c4e0861ebe26495eb746ba5)

Reverted event priority, even cancelling. It caused issues with other
plugins, like Coreprotect.
Also fixed an issue with chests being accessable, even if there's a
block on top.