Description:
Moved NVIDIA_Optical_flow sample app and comparison app to
opencv_contrib branch. Added CUDA_CUDA_LIBRARY in CMakeLists.txt for
resolving linker errors.

from MSVS2017 and GCC8 -O1 mode

- exception safe smart pointers, fixed many memory leaks
- fixed errors handling
- fixed strings handling
- fixed file existence check
- fixed toFraction() implementation
- add 'drop=true' for v4l2 input
- avoid overriding custom pipelines sink's 'max-buffers' value
- updated valgrind supression rules
- added support for GStreamer native leaks tracking (via gst_deinit() call)
- repaired capturing through GStreamer0.10 (fixed CV_8UC1)

causes leaks if FFmpeg is disabled through OPENCV_VIDEOIO_PRIORITY_FFMPEG=0

 -

* Introduce GAPI_TRANSFORM initial interface

Comes along with simple tests and kernel package changes

* Fix documentation and adjust combine() function

* Fix stuff after rebasing on master

* Remove redundant functionality

* Refactoring according to review feedback provided

* Fixes according to review feedback

* Reconsider transformations return and fix a warning

* Fixes from code review

* Add a new simple test

* Cleanup, added tests on GScalar, GMatP, GArray

Test request by #14583 (#14800)

* add test to show the undistort bug

* move test to calib3d