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.

objectives_label.gd

@@ -0,0 +1,8 @@
+extends RichTextLabel
+
+# Called every frame. 'delta' is the elapsed time since the previous frame.
+func _process(delta: float) -> void:
+	var new_text = "OBJECTIVES:\n"
+	for objective in %Player2D.objectives:
+		new_text = new_text + %Player2D.objectives[objective]
+	text = new_text