Break out cpu-specific and gpu-specific code from RenderWebGL.js file

[fsih]

The renderer may use the CPU or GPU depending on the processing power of the machine it's running on. There is a bunch of code that does the same stuff for the CPU and GPU paths, e.g. implementation of touching color. Many bugs come from the fact that these 2 paths are out of sync

It's difficult to parse RenderWebGL.js and easily see which code is shared by both paths, which functions are CPU specific and which functions are GPU specific. Breaking out the specific code into their own files would more easily ensure that when you fix one you need to fix the other and which code is shared.