Added new Intel-optimized 3x3 and 5x5 kernels to medianFilter.cl file and corresponding code to host in smooth.cpp

Only Intel platform and 1 channel images are supported.
Moved new kernels under conditional compilation to disable their build for 3-channel images; added condition to use new kernels only for images that are big enough
Adding explicit variable conversion in ocl_medianFilter() to suppress build errors on Linux & Mac
Added condition to use optimized kernels for images of size that multiple of 4 only
Merge pull request #2794 from mletavin:pullreq/140516-median