OCL: matchTemplate: added support for 3-channels

check_regression=*OCL*MatchTemplate*
test_modules=imgproc
build_examples=OFF

added support for 3-channels for all methods
changed  kernels for `CCOEFF` and `CCOEFF_NORMED`
for `CCORR` added implementation using `dft`, called when the `template size >= 18`
for `SQDIFF` added implementation using `CCORR`, called when `template size >= 18`
`OpenCV` already has OpenCL version of `cv::extractChannels`.