This allows to work around removed CubeGeometry sides functionality.

Now we can finally mess with car materials directly in the scene file.

Also, removed webgl_trackballcamera_earth as there is already a example showing the usage and another one using this scene.

Also, removed GeometryLoader. I'll try doing the JSONLoader to GeometryLoader change again in the future.

@alteredq: I'll try to tackle Minecraft AO next.

See #2623.

Without CubeGeometry is a little bit easier to follow. Wasn't sure whether doing it like this or using a single material/texture with modified UVs per side.
Also, I've had to comment out some code from GeometryUtils that asumed object2 to be a mesh.

This way the panel illustrates the API better.
It's not too intuitive but eventually the (future) helper will probably make it uneeded.

Ok, lets go with blue.

Still not happy about it, need more time to see what the right style for all this is.

I wonder what to do about geometries and materials used by removed objects. Seems like we would need to implement some reference counting scheme (we can't just remove deleted object subcomponents as they could be shared).