G-API planar kernels (#14917)
* Added resizeP with tests
* NV12 planar filters
* fix warnings in ResizeP test
* fix out mat ocv warning
* sz_on - > sz rename
* cpu tests new signature
* try to fix resizeP test
* trailing spaces remove
* doxygen doc fixed
* doxygen minor fix
* more doxygen fixes
* Doxygen corrected and extended after review.
* Add Sobel kernel which returns both dx and dy
* Splice dx and dy and extend add_border function
Also change some tests parameters
* Add borderValue parameter in test
* Introduces fluid kernel for sobelxy
Adds tests (basic and performance) on new backend
* Introduces BufHelper struct for some arithmetic
* G-API Initial code upload
* Update G-API code base to Sep-24-2018
* The majority of OpenCV buildbot problems was addressed
* Update G-API code base to 24-Sep-18 EOD
* G-API code base update 25-Sep-2018
* Linux warnings should be resolved
* Documentation build should become green
* Number of Windows warnings should be reduced
* Update G-API code base to 25-Sep-18 EOD
* ARMv7 build issue should be resolved
* ADE is bumped to latest version and should fix Clang builds for macOS/iOS
* Remaining Windows warnings should be resolved
* New Linux32 / ARMv7 warnings should be resolved
* G-API code base update 25-Sep-2018-EOD2
* Final Windows warnings should be resolved now
* G-API code base update 26-Sep-2018
* Fixed issues with precompiled headers in module and its tests
