Make it so that lights bounce off of mirrors

[b-x-wu]

Right now, when a light hits a mirror, that light is not reflected to light other objects.

To do so, light that bounces off a mirror should become a light source in the scene. When a mirror is added, compute the new light sources that are created from light bouncing off the mirrors. When a mirror is removed, remove the light sources emanating from that mirror. (Light sources can be tagged with the mirror it comes from.) When a light source is added, compute the new light sources that are created from the new light bouncing off the mirror.

There should be a new light source type that allows for an area of origin. See the images below.