Detect render engine and use proper materials rather than using a checkbox

I do not want to create extensive code for materials, but I do want
materials no matter what engine. That's why all Non-Cycles engines are
under the else block. POV-Ray is listed only because I tested the code
with it.
Merge pull request #12 from le717/detect_render_engine

Detect render engine and use proper materials rather than using a checkbox