Would be nice to be able to create and add imageless Sprites to scenes.

[icarito]

This way I could interactively a sprite to a scene and then add the image, without having to define a subclass. (Get rid of NoImageError). What Pilas does is that it offers a stock image in this case.

[acbart]

I'm not against this - @rdeaton, what do you think? I think it might be less punishing to novices too, who forget to make an image.