Create generic shader manager and generator

[recp]

A shader manager could provide a compiled program or collect combinations of shaders then compile them as program.

This will be used for COMMON profiles/techniques.

• [ ] Shader manager
  • [x] Shader manager for common materials; mesh/primitives must use same program/shaders if all attribs, features are same
  • [ ] Custom shaders?
• [x] Shader generator
  • Shader generator common materials
    • [x] constant
    • [x] lambert
    • [x] blinn
    • [x] phong
  • [x] Shader generator PBR materials
    • [x] Metallic-Roughness
    • [x] Specular Glossiness