Simple implementation of StereoBM_GPU.
It is excluded from compilation now. 

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

Fixed CMake cached variables

 "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)