Blender Git Loki

OpenColorIO: Improve/Cleanup Implementation

This split the shader cache into caches for Shader, Lut and CurveMapping.

This way we can have smoother updates when tweaking/animating the color
managment (i.e. exposure and gamma should only recompile the shader).

The curvemapping, predivide and dither options are no longer compile time
optimized but use uniforms. I did not measure any performance difference.