Bug 2047: adding images to arbitrary authorized values

Bug 2047: adding images to arbitrary authorized values

I've refactored the subs I added in the previous commit so that they make a little
more sense and are in better places in the code base. I was really hoping to make use
of existing subs, but they all seemed so specific to particular uses.

The icons now show up on the OPAC item details page.

TODO: The icons still don't show up in the OPAC search results page.

Signed-off-by: Joshua Ferraro <jmf@liblime.com>