Add Material class

[raysinm]

Should contain color(s) -for filling
The material should consist of emissive, diffuse
and specular colors. Allow the user to change the different colors.
Uniform/ Non-uniform versions!

• Add a uniform material for each model. The material should consist of emissive, diffuse
  and specular colors. Allow the user to change the different colors.
• Add at least one non-uniform material (i.e. a material that is different on different
  vertices). There are many different options here so be creative.
• Can be implemented after the lecture on Illumination Models.