Implemented base for the virtual desktop system

- Virtual desktop based on a DIV fixed element taking all visible space on
  the page
  -> For the moment, the Got it! javascripts for the virtual desktops will
     not work on sizes other than 100% of the page (width and height)
  -> All DIVs structure for the virtual desktop is generated after page
     load (allowing a loading bar while generating it)
- Frames content load is AJAX based
  -> Way faster than reloading all the pages (local test: 1 sec. for 2 MB)
  -> Should keep the virtual desktop state in session in the future
- Javascripts of Got it! are based on the Module pattern
- Renamed desktop.css to gotit.desktop.css (namespace)
- Changed gotit.desktop.css to add elements usefuls for resizing frames