Preliminary support for DICOM (*.dcm) files.

Still have to deal with *magick weirdness with different files.
GraphicsMagick barfs on some, ImageMagick on others. Tilepic generation
is also not working.
Added DICOM mime type to media_display.conf

You wouldn't believe how long it took me to figure out that this was
causing the DICOM/DCM tilepic display to not work properly.
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
Undo last change
Merge branch 'master' into ct_scans
Interim commit of previous work related to creating multipage tiffs from zip/tgz archives
Merge branch 'master' into ct_scans

Conflicts:
	app/conf/media_display.conf
ImageMagick, Imagick and GraphicsMagick plugins now create a multi-page tiff from an uploaded zip or tgz archive as 'fake' original.

Gmagick unfortunately does not as I couldn't get it to create a
multi-page object.
Make sure temporary files are all removed