This commit integrates support of OpenColorIO library into build systems.
It also contains C-API for OpenColorIO library which could be used by Blender.
CMake has got find rules familiar to OpenImageIO's one which makes it easier
for build system to find needed libraries and includes. Scons only could use
explicitly defined paths to libraries and includes.
C-API would be compiled and Blender would be linked against C-API and OpenColorIO
but it wouldn't affect on Blender behavior at all.
OpenColorIO could be disabled by setting up WITH_OCIO to Off in CMake and
setting WITH_BF_OCIO in Scons.
