New particle system

yay
So this is for scene_graphnode#setLookVector: we have a setWorldTransform method so since you added a similar method
there (which btw should be named setFromLookVector like all the other
setter methods) you can set it like that in your code - no need for a
setLookVector method in the scene_graph. Again the aim is to keep the API
minimal and not have methods for special cases.