Moved userdata to XDG_DATA_HOME

Moved the current default userdata location to $XDG_DATA_HOME or ($HOME/.local/share if not available), as per the base directory specification ( http://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html ).

Adjusted launch script to migrate from both ~/.kodi and ~/.xbmc to $XDG_DATA_HOME.

Hopefully that's all.