Performance: sharedbuffergeometry update ranges

[avaer]

The brush geometries seem to be 1 MB, re-uploaded on every tick. That's pretty taxing for 90FPS.

This sets the updateRange for brush geometries, so in most cases only a little bit of the geometry is uploaded by THREE.js (exactly as much as we have drawn).

Without this I was unable to hit 90FPS when drawing, even with straight OpenGL. But with, it it seems very smooth.

[msub2]

@dmarcos This can be closed since I included this fix in #265