Faster scene building for many emitters

[OnoSendai]

Not sure if anyone had noticed, but scene startup was quite slow when there were many emitting objects (e.g. 10K objects).
I've optimised the startup for such cases: This scene used to take 37s to startup, and now takes 1.7s.
(scene has 10k emitting sphere meshes)

cheers!

[Zom-B]

Speedups are always welcome, even if can count the lightsources in my scenes can be counted on one hand ^^

Nice scene, is that motion blur in action?! Some AD or Bokeh version would be nice to look at

[OnoSendai]

Yes, that's motion blur