Display vertex colors from OBJ file

[elsurudo]

Apparently, there is a pseudo-standard for storing color data along with each vertex in OBJ files:

It looks something like this:

v 1220.094482 -572.500000 177.713943 0.984314 0.764706 1.000000

where the last 4 numbers represent RGBA, from 0 to 1.

From: http://gamedev.stackexchange.com/questions/21303/how-can-i-include-vertex-color-information-in-obj-files/66270#66270

Scanning this data is easy enough. I am willing to make a PR with these changes, but could use a hint as to what needs to be changed in GLModel's draw method to actually draw the colors.