* custom OpenCL G-API kernel draft

* clean up and warnings fix

* more warnings

* white space

* new blank line at the EOF removed

* HAVE_OPENCL guard

* remove unnecessary ocl API call

* remove sum test workaround

* check if opencl activated

* fix std::str warning

* CPU fall back for symm7x7

* gpu test kernel draft

* adjust have opencl guard

* more guards

* one more attempt to adjust guards

* empty stub files and kernel source files creation in the test directory

* try to force auto generation

* one more attempt to force build

* remove symm7x7 custom from gapi module

* looks like that this version works properly on Win desktop

* clean up

* more clean up

* address some suggestions from Dmitry's review

* const kernel coefficients

* CV_Error in kernel + try to fix cpu fallback

* CV_Error_ instead CV_Error

* everything in one gapi_gpu_test.cpp

* fix warning

* remove kernel generation, add kernel string

* avoid generated code and ocl internal namespace

* fix misprint

* c_str

* dnn/Vulkan: don't init Vulkan runtime if using other backend/target

Don't need to explictly call a init API but will automatically
init Vulkan environment the first time to use an VkCom object.
Signed-off-by: Wu Zhiwen <zhiwen.wu@intel.com>

* dnn/Vulkan: depress compilier warning for "-Wsign-promo"
Signed-off-by: Wu Zhiwen <zhiwen.wu@intel.com>

introduced by commit 4e629000

  - add infrastructure support for Power9/VSX3
  - fix missing VSX flags on GCC4.9 and CLANG4(#13210, #13222)
  - fix disable VSX optimzation on GCC by using flag ENABLE_VSX
  - flag ENABLE_VSX is deprecated now, use CPU_BASELINE, CPU_DISPATCH instead
  - add VSX3 to arithmetic dispatchable flags

* Added caching of agents execution sequence

* Merged linesRead() and nextWindow() methods on FluidAgent in one method

* Added caching of input lines for fluid::View

* Added caching of output lines for fluid::Buffer

* Fixed GAPI_Assert to work in standalone mode

This MR fixes this.

GAPI (fluid): RGB to Lab optimization (#13206)

* GAPI (fluid): BGR2LUV, RGB2Lab: performance test

* GAPI (fluid): BGR2LUV, RGB2Lab: using cv::hal::cvtBGRtoLab

* GAPI (fluid): BGR2LUV, RGB2Lab: hide reference code with #ifdef

GAPI (fluid): RGB to YUV optimization (#13174)

* GAPI (fluid): RGB to YUV: activate performance tests

* GAPI (fluid): speedup 4-8x RGB-to-YUV, 2.5x YUV to RGB with int16 arithmetic

* GAPI (fluid): RGB <--> YUV: fixed compiler warning

* GAPI (fluid): RGB <--> YUV: additional speedup 2-3x times (10-15x over original) via manual CV_SIMD

* GAPI (fluid): RGB <--> YUV: dynamic CV_SIMD dispatching

OpenCV 4.0.0

OpenCV 4.0.0 for Intel(R) OpenVINO(TM) toolkit

OpenCV 3.4.4

OpenCV 3.4.4