G-API: Implement color-convert kernels (#14513)

* Implement color-convert kernels

* Fix rgb2yuv422 reference version

* Fix comments to review

* Restore NV12toBGR in imgproc.hpp

* Add accuracy tests

* Fix doxygen

* Fix ref version yuv422

* Fix warnings

* Fix typos

* Fix simd version yuv422

* Fix warnings

* Fix compile error

* Fix warning

* Remove comment

* java: fix java SimpleBlobDetector

* add SIMPLEBLOBFeatureDetectorTest

* add package org.opencv.test.features2d;

* fix SIMPLEBLOBFeatureDetectorTest

* cast positional arguments to int

* Changed to integer division based

* removed white space

* removed white space

backporting of commit: 76fca0e7

* Add Axpy layer

* Fix test

* fix caffe importer

Fix build issue on QNX platform (#14678)

* QNX compatibility

* core: unify gettimeofday() usage

* Revert the bad parts of b085158d to fix https://github.com/opencv/opencv/issues/11131
but preserve the good parts to keep https://github.com/opencv/opencv/issues/10791 fixed

* calib3d: add regression test for stereoCalibrate to fix https://github.com/opencv/opencv/issues/11131

because t = (time.time() - t) will return seconds,  dividing by 1000 to obtain seconds will be incorrect.

G-API: Add parameters alpha and beta in tests on ConvertTo kernel (#14684)

* Add parameters alpha and beta in tests on ConvertTo kernel

* Change tolerance function

* Reduce number of test cases

https://github.com/protocolbuffers/protobuf/compare/v3.5.1..v3.5.2