* 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
