GAPI (fluid): Median blur optimization (#13329)

* GAPI (fluid): Median blur optimization: reference 3x3

* GAPI (fluid): Median blur optimization: CPU dispatcher

* GAPI (fluid): Median blur optimization: manual CV_SIMD

G-API rename GPU backend to OCL backend (#13240)

* renaming draft

* inline namespace instead non-safe define

* more back compatibility

* Updates after review from Dmitry

GAPI (fluid): Erode/Dilate optimization, part 2 (#13319)

* GAPI (fluid): Erode/Dilate optimization: hard-code 3x3 case

* GAPI (fluid): Erode/Dilate optimization: CPU dispatcher

* GAPI (fluid): Erode/Dilate optimization: speed-up 10-15x times with CV_SIMD

* GAPI (fluid): Erode/Dilate optimization: 20-30% speed-up

GAPI (fluid): Erode/Dilate optimization (#13315)

* GAPI (fluid): Erode/Dilate optimization: hard-code 3x3 case

* GAPI (fluid): Erode/Dilate optimization: CPU dispatcher

* GAPI (fluid): Erode/Dilate optimization: speed-up 10-15x times with CV_SIMD

GAPI (fluid): Filter 2D optimization (#13290)

* GAPI (fluid): Filter 2D optimization: speedup 13x if float, 2x if integral

* GAPI (fluid): Filter 2D speedup 8x if output is short/ushort

* GAPI (fluid): Filter 2D speedup 7x if output is uchar

* GAPI (fluid): Filter 2D optimization: fixed compiler warnings

* GAPI (fluid): fix compiler warnings on Mac

* GAPI (fluid): fix compiler warnings on Mac

* GAPI (fluid): fix compiler errors on VS2015

* GAPI (fluid): fix compiler errors on VS2015

* GAPI (fluid): fix compiler errors on VS2015

More fixes for G-API tests (#13251)

* scalar comparator and more fixes for tests

* add weighted aligned

* white space

* more white space

* Add weighted test accuracy check enabled

GAPI (fluid): optimization of Separable filter (#13221)

* GAPI (fluid): Separable filter: performance test

* GAPI (fluid): enable all performance tests

* GAPI: separable filters: alternative code for Sobel

* GAPI (fluid): hide unused old code for Sobel filter

* GAPI (fluid): especial code for Sobel if U8 into S16

* GAPI (fluid): back to old code for Sobel

* GAPI (fluid): run_sepfilter3x3_impl() with CPU dispatcher

* GAPI (fluid): run_sepfilter3x3_impl(): fix compiler warnings

* GAPI (fluid): new engine for separable filters (but Sobel)

* GAPI (fluid): new performance engine for Sobel

* GAPI (fluid): Sepfilters performance: fixed compilation error

Add URLs, harmonise formatting, and fix parse error in bibliography (#13228)

* Fixed parse error in bibliography

* Removed extra curly braces

* harmonized whitespace

* changed organisation -> publisher where appropriate. Organisation is intended as the author's organisation, not the publishing.

* harmonized capitalisation and whitespace

* Add links to about 1/3 of references

Use a global dedicated mutex to make sure initialize once and
protect command buffer pool and queue.
Signed-off-by: Wu Zhiwen <zhiwen.wu@intel.com>

created from RAW memory buffers (without proper lifetime management)

- don't require "OPENCV_PYTHON{2,3}_INSTALL_PATH" if OPENCV_SKIP_PYTHON_LOADER=ON
- avoid unnecessary relative paths in generated config-X.Y.py

* cmake: install 'legacy/constants_c.h' files

* samples: add compatibility test code

Reduce input size for OpenPose tests