Changed VectorDescriptorMatch interface to add factory capabilities and changed factory functions interface (return smart pointer)

- 3 new points mostly done:
      - OpenGL support enabled (windows are rendered using GPU)
      - Save current screen (with overlay and so on...) with shortcut CTRL+S
      - Text rendering (with any system font, and possibility to set the style - normal, italic,... - the weight - normal, bold, ... - the color, the spacing between letters, and so on...)

fix warnings about missing destructors in FeatureDetector and DescriptorExtractor classes and their derivatives

 "error: explicit template specialization cannot have a storage class"

- Save current screen (CTRL+S), with png, jpg, jpeg, bmp format support
- OpenGL rendering enable (make Qt very fast)
      -> working on opengl callback (done soon)
- Rendering optimised (with and without openGL)

Corrected Mask operator (from documentation mask must be a char matrix with non-zero values in the region of interest)

- fixed bug ticket #412

- save/load window parameters implemented !

fixed the output disparity at the extreme cases (minDisparity or minDisparity + numOfDisp - 1). Thanks to Patrick Mihelich for the report (trac #395)

- imgregion shortcut implemented (CTRL+O)

- imgregion (as with Matlab) implemented

- aspectRatio is controled by cvSet/getWindowProperty

- fix CMake OpenGL compilation

- fix zoom offset of 0.5
- fix CMake problem with QT detection
- Code optimisation