Use tone mapping to not get blown out colours

[davepagurek]

Right now when things get too close to lights, we get large white spots where the additive light goes over the maximum value.

A simple fix is to drop in John Hable's tone mapping function:
https://github.com/davepagurek/everything/blob/master/src/commands/composite.js#L60-L68

We can add this into our createDrawObjects shader before setting gl_FragColor.