This reverts commit 54a202b3.

Conflicts:
	modules/core/doc/command_line_parser.rst
	modules/core/include/opencv2/core/core.hpp
	modules/core/src/cmdparser.cpp
	modules/gpu/perf/main.cpp
	modules/gpu/test/main.cpp
	modules/ts/src/ts_perf.cpp

This reverts commit e2d9fc4d.

This partly reverts commit 6ca61827.

This reverts commit eb4ce67d.

Conflicts:
	samples/android/color-blob-detection/src/org/opencv/samples/colorblobdetect/ColorBlobDetectionView.java

* 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

+ Some minor formatting fixes.