Beam billboards

Axis-locked beams. Would just need to have a proper Object3D.getVG() class version of this so that it can work under dynamic BSP depth sorting in Alternativa3d.

Beams are single-faced objects that are always oriented to face the camera along their beam axis.

I know cones can be used for beams as well, but they use more polies. 

The disadvantage of beam billboards is that if the camera look vector is collinear with the beam vector, you won't get to see the beam.  However, they work ok for visible beams/tracers/lightsabers coming in from partially from the side, and are still visible. 