[WIP] BulletEngine

Depends on #563 #568 
Fixes #414 

Code still needs cleanup and doc, maybe Line::intersects() can be optimised, but here it is: the BulletEngine

* Bullets of one kind are handled by the BulletEngine, if they have general.instanced=true
* The BulletEngine draws Bullets of one kind instanced. That means more rendering performance and almost no overhead (which was quite significant for me) creating those bullets.
* InstancedBullets are moved much more efficient, using just one Line-WorldTreeQuery per frame


Please test it and report back. Expect significant improvements in the F2 battle, but there are still perfproblems with splitdetection and in VoxelRenderData::updateBuffer() (when using the homebase)