add basic functionality for adding group items

UI/Components/OverrideEditorSettingsMenu/OverrideEditorSettingsMenu.gd

@@ -26,3 +26,10 @@ func get_overrides() -> Dictionary:
 		res.merge(item.get_property())
 
 	return res
+
+
+func clear() -> void:
+	override_item_container.get_children().map(
+		func(c: OverrideEditorSettingsMenuItem):
+			c.queue_free()
+	)