Merge pull request #22 from badshah400/master

Replace Imagemagick by ristretto -- xfce's lightweight image viewer
make some space on the promo dvd
need more space on promo dvd
Drop XFCE-MINIMAL; XFCE-BASIS is now the minimal XFCE.

1. Keep only the base requirements for an Xfce desktop in XFCE-BASIS,
   move everything else to XFCE
2. Move applications in XFCE-MINIMAL (and required for rescue CD) but
   not part of core Xfce to REST-CD-X11 (file-roller, etc)
3. Make pattern rest_cd_x11 depend on XFCE-BASIS instead of XFCE-MINIMAL
4. Remove dependence of xfce_basis on XFCE-MINIMAL.