Created a XDG class to load XDG_ environment variables
Created a DesktopEnvironment class to detect the desktop environment
Renamed the GNOME integration to default Linux integration

Because KDE and other desktop environments should use SWT
integration and FreeDesktop integration there's no need to have
the same sub integrations for different desktop environments.
This default Linux integration will be de base for Linux integration
using SWT and FreeDesktop.