Merge pull request #21 from badshah400/master

Add file-roller to XFCE-MINIMAL; grsync, lftp, gnu_ddrescue to REST-CD
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.