SLG4: first implementation of Sobol Sampler

--HG--
branch : slg3.5_startup
rename : src/utils/sampler/sampler.cpp => src/utils/sampler/sobol.cpp
SLG4: Added Cranley-Patterson rotation to Sobol Sampler

--HG--
branch : slg3.5_startup
SLG4: fixed a bug recently introduced in Glass material (CPU-only)

--HG--
branch : slg3.5_startup