This fixes build without TBB and CUDA. Issue #2445

* 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

added recommended number of stripes to parallel_for_, modified some of the functions to use larger stripes (for better performance)

added cross-platform Mutex implementation; enable platform-native (GDC/Concurrency) parallel_for_ implementation when TBB is not installed.