Add objectives listing and all four data disks/tablets.

Track each individual disk and ensure they are loaded in order.
Player can collect multiple disks in one run but must present them
to the pharaoh in order.

disk.gd

@@ -4,4 +4,5 @@ extends Pickup
 
 func _on_picked_up() -> void:
 	%Player2D.give_disk(disk_num)
+	%Player2D.give_objective("disk%d" % disk_num, "Install data disk %d" % disk_num)
 	print("Picked up disk ", disk_num)