added 3 channels support to cv::bilateralFilter

Conflicts:
	modules/imgproc/test/ocl/test_filters.cpp
added 3-channels support to cv::boxFilter, cv::blur, cv::sqrBoxFilter
added 3-channels support to cv::filter2D, cv::Laplacian
added 3-channels support to cv::medianBlur
refactored filter2D; eliminated restrictions sdepth == ddepth, delta == 0
Merge pull request #2523 from ilya-lavrenov:tapi_filters