Right now we have dangerzene-processed/, dangerzone-rejected/,
dangerzone-processing/... that's noisy, at best, and dangerous, at
worst: at least one user thought that dangerzone-processed was where
processed (so: safe) files ended up.
Just have dangerzone/ and safe/ folders at the toplevel, with the
processed/, rejected/, processing/ stuff inside dangerzone/.
Closes: #4 (closed)