WaveFrontReader update to support per-vertex color extension

[walbourn]

While more of a 'hack' than an extension, some tools support exporting/importing WaveFront OBJs with per vertex color thrown in

####
#
# OBJ File Generated by Meshlab
#
####
# Object VERTEXPAINT_004_OBJ.obj
#
# Vertices: 284
# Faces: 281
#
####
mtllib ./VERTEXPAINT_004_OBJ.obj.mtl

vn 0.029683 0.730087 -0.682709
v 1220.094482 -572.500000 177.713943 0.984314 0.764706 1.000000  

# "3 vals for Vert and 3 vals for Col"

vn 0.000000 0.858139 -0.513418
v 1291.571533 -609.439636 -28.628490 0.921569 0.219608 1.000000
vn 0.303129 0.896367 -0.323480

https://gamedev.stackexchange.com/questions/21303/how-can-i-include-vertex-color-information-in-obj-files