Make game objects you can interact with more "visible"

[jakory]

Currently, there is no clear way of knowing which game objects in a scene are draggable or able to be interacted with without just trying all of them.

We should add some way of easily seeing which objects in the scene are draggable or able to be interacted with. In one previous app, we added a grow-shrink pulse motion to each of these objects (so the object would "pulse" in place), but that caused havoc with the collision detection.