Reimplement thread management functions:
Reimplement thread management functions:

* Refactor auto-detection of parallel frameworks
* Implement cv:getNumThreads, cv::setNumThreads and cv::getThreadNum for all supported frameworks
* From now cv::setNumThreads(0) can be used to turn off parallelisation

apavlenko/opencv,opencv/opencv,apavlenko/opencv,opencv/opencv,opencv/opencv,apavlenko/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,opencv/opencv,apavlenko/opencv,apavlenko/opencv,opencv/opencv,opencv/opencv,apavlenko/opencv