T-API: optimization of cv::accumulate, cv::accumulateSquare, cv::accumulateProduct, cv::accumulateWeighted; added strategies in cv::predictOptimalVectorWidth

**Performance report:**
http://ocl.itseez.com/intel/export/perf/pr/2956/report/

check_regression=*OCL*
test_filter=*OCL*
test_modules=imgproc,core
build_examples=OFF
For this case I believe that more clear decision is to **export** separate functions for different strategies.
Also passing strategy after 8 optional arguments doesn't look good.