umat: fix memory leaks
fixed UMat::copyTo(UMat)
Merge pull request #2004 from ilya-lavrenov:tapi_umat_copyto
Merge pull request #1997 from alalek:tapi_fix_memleaks
adding LICENSE file and a sample of its reference in ocl.hpp
Merge pull request #2000 from apavlenko:license_copyright