Issue 8647: Updated doc for cv::matchTemplate to reflect current support for methods when mast template is supplied.

Updated comments for cv::ellipse and cv::ellipse2Poly to clarify some behaviour that has confused some users.

Amend: Delete trailing whitespace to make doc tests happy

* Improve documentation.

* Update imgproc.hpp

Make it more clear for the type of input argument.

 - let it possible to reach Bayer2BGRA conversion

Extended parallel version to all frameworks supported by OpenCV;
Added some documentation notes in modules/imgproc/include/opencv2/imgproc.hpp;

* Add Grana's connected components algorithm for 8-way connectivity. That algorithm is faster than Wu's one (currently implemented in opencv). For more details see https://github.com/prittt/YACCLAB.

* New functions signature and distance transform compatibility

* Add tests to imgproc/test/test_connectedcomponents.cpp

* Change of test_connectedcomponents.cpp for c++98 support