- added cRay::mDistance
- added cRay getter and setter for mOrigin and mDirection
- added Button to start render process
- made ImageViewer static public
- added global variables to define left, right, top and bottom borders of
  the rendered screen
  - added drawing of coordinate axes in raytracing window
  - added test code to show, how the rays are getting shot in the
    raytracer window
    - added standard constructor for cRay
    - changed cRay::fShot (not finished yet)
    - changed fDraw function of cRay
    - added class cRender; thought as a superior render class to handle
      the whole rendering process
      - deleted some commented stuff
      - added a extra thread for the rendering stuff, so everything else
	works properly, while the render process is working