* Remove "simple" flow estimation from help (because it was disabled by 653bca8b)
* Add `flush` after printing iteration number for better UX

compute() for BP and CSBP output 32-bit floating-point mat, and in cv::imshow() 32-bit floating-point is recognized as [0,1] and maped to [0,255], that causes gray window for BP and CSBP.

Original commit is a5f19f7dd6ae5bc93f73e0417a9e0bfd34c01672

in this case the sample will not be built if OpenGL is not found

(cherry picked from commit ff002203)

As is it was not possible to use CUDA.

changed hog to work with variable parameters and changed the hog sample to test it with more options

added comments and tests

Conflicts:
	samples/gpu/video_writer.cpp