opengl and serialization test updates

[headupinclouds]

opengl related acf fixes and …

• support chnsCompute + isInit: see #37
• support rgb-to-gray w/ correct channel count==1 : see #36
• *.mat serialization testing
  • download Inria/Caltech *.mat toolbox pedestrian models from github storage using cmake/hunter_private_data
  • add simple serialization tests in test-acf GTest code (more rigorous testing needed)
  • remove unused code blocks and some debug code in test-acf.cpp
• fix a boundary case in sse gradHist() code
• remove unused conditional cv::cvtColor() code blocks in rgbConvert.cpp
• add virtual destructor to ObjectDetector.h base class
• support acf shrink (via constructor input) in the GPUACF code
• update gradhist glsl shader to highp precision
• unify header include style
• remove various comment blocks + format fixing
• add acf special member isLuv to indicate special case input LUV processing (such as in gpgpu pipeline)
• provide naive GLDetector : public acf::Detector naive detector to exercise shader code in acf-detect
  • use aglet lib for portable context
  • compute acf pyramids from input cv::Mat (in practice this would be separated for efficiency