Adds a proper permission check to make sure players are allowed to teleport through the artificial portal
Adds a teleportation back to the entrance as the teleportation event cannot be properly cancelled
Adds a proper class for storing info about the teleportation
Adds all chunk unloading to a queue
Adds a thread which unloads chunks
Updates chunk unload requests such that a chunk won't be unloaded twice,
and an old unloading request cannot unload a chunk too soon
