Added utility to detect zip and gzipped tar archives (and probably a lot more)
Add support for zip and gzipped tape archives to media processing backend.

What it does is it takes the first file it encounters inside the
archive and generates a preview from that. All other files (including
the above 'primary') are added as multifiles to the newly created
representation, if possible (i.e. if file format is supported).
Remove related multifiles when representations are deleted