Replace Imagemagick on REST-CD-X11 by ristretto on XFCE-MINIMAL.

Ristretto is a rather lightweight image-viewer, and this swap allows us
to shave a few MB's off the rescue CD.
Add xfce4-appfinder to XFCE-MINIMAL pattern.
Merge pull request #22 from badshah400/master

Replace Imagemagick by ristretto -- xfce's lightweight image viewer