Controlled particles: automatic frustum culling?

[hmans]

When you have a controller particles effect with lots and lots of particles spread across the world, it could be fun to automatically cull these -- ie. from the many many asteroids we already have, only upload those to the instance matrix that are in view, and cap InstancedParticles.count to the number of instances rendered.

(Not sure if this really yields any performance benefit. Asteroids could just as well be separate instancedmeshes, and we'll let Three's own culling do its thing?)