Fix cudacodec::VideoReader::nextFrame python bindings
* Signla to python bindings generator that nextFrame's OutputArray is a GpuMat.
Also remove duplicate test in cudacodec
* cudacodec: drop CV_GPU, wrap GpuMat only
* Make it explicit that frame in nextFrame is GpuMat and cannot be multiple types as implied by OutputArray
OpenCV fix 14774 breaks cudacodec
* Example to describe comilation issue
* Added required changes, builds with -DWITH_FFMPEG=ON|OFF
* Working with standard ffmpeg cap.
* Changed cudacodec to use new retrieveRaw() function, to retrieve the raw encoded bitstream, from the videoio module instead of its own implementation.
* Fix cv::cudacodec::VideoWriter
* Update to use VideoContainer
* Remove header used in testing
* Remove warning
* remove dependence on redundant ffmpeg codecs
* cudacodec: use .set(CAP_PROP_FORMAT, -1) to extract RAW streams
* whitespace
* addressed alalek's comment
