Modified base materials to utilize uLightColor

<h3> Reason

To resolve requests: https://github.com/MasDennis/Rajawali/issues/225 https://github.com/MasDennis/Rajawali/issues/324

Rajawali has had the ability to set the light color, but the materials were not utilizing the light color.

<h3> Method

The accepted equations for calculating light and texture color are as follows:

ambient = Ka x globalAmbient
diffuse = Kd x lightColor x max(N · L, 0)
specular = Ks x lightColor x facing x (max(N · H, 0))

While the `PhongMaterial` followed this fairly closely, `DiffuseMaterial` was quite different. I went ahead and reworked `DiffuseMaterial` just to start giving some unifiormity to the material classes.

<h3> ToDo

-Extend this format to all material classes