small cleaning

Added to the tutorials the "Support Vector Machines for Non-Linearly Separable Data" contributed by Fernando Iglesias García. Corrected a mistake in the gpu-basics-similarity.rst file. 

Added the "Similarity check (PNSR and SSIM) on the GPU" tutorial. Corrected an highgui TOC tree mistake.

python cv2 MLP sample done

Added the How to create videos with OpenCV Tutorial. Made some corrections to the feature2d, to get rid of some documentation build errors. 

minor cleaning

* Fixed display of struct and class definitions (except classes with base class specified).
* Fixed formatting and referencing errors in several documentation files.