fix(example): prevent menu cube from detaching on activation

The example scene `019_ControllerInteractingWithPointer` has a menu
cube that is displayed when the app menu button is pressed. However,
due to some previous changes, the cube has it's parent reset due to
the `LoadPreviousState` method defaulting the parent to null.

The solution is to ensure `SaveCurrentState` is called so it always
knows about it's parent.

Author: thestonefox

Assets/SteamVR_Unity_Toolkit/Examples/Resources/Scripts/Menu_Container_Object_Colors.cs

@@ -15,5 +15,6 @@ protected override void Start()
     {
         base.Start();
         SetSelectedColor(Color.red);
+        SaveCurrentState();
     }
 }