remove brick renderer from vvTexRend

we have vvSerBrickRend and vvParBrickRend to replace it
remove 2d texture based renderers and spherical 3d textures
remove register combiners and paletted texture support
multiple independent transfer functions for multi-channel data
also get rid of ARB_fragment_program

glsl is just as fast since we also use less than 4 bytes/voxel
enableShader has to happen after updateLUT

enableShader sets up texture bindings, which updateLUT would change
use MultiDrawArrays instead of Begin/End