Bug 9174: Fix itemtype image display in OPAC lists

Bug 9174: Fix itemtype image display in OPAC lists

Prior to this patch, C4::VirtualShelves::Page did not make sure that
the itemtype images that it chose when displaying itemtype images for
biblio-level itemtypes were for the correct interface, so
even on the OPAC the Intranet icons were requested. On standard
installations, intranet-tmpl is not available to the OPAC.

To test:
1) Set noItemTypeImages to "Show" and item-level_items to "biblio record"
2) Create a list and add an item with the default item type (942$c in
   MARC21) set to something with an itemtype image associated with it.
3) View the list in the OPAC.
4) If you are an a standard install, the itemtype image will be a broken
   link. If on a dev install, you can confirm with Firebug or the like
   that the image is pulled from /intranet-tmpl.
5) Apply patch.
6) Run `prove t/db_dependent/Koha.t` to confirm that the behavior of the
   routine used to retrieve the image URL is correct. (Note that you
   must have an item type with the code 'BK')
7) Refresh the list, noting that the display is now correct/the image is
   pulled from opac-tmpl.

Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
It works as expected. All tests in Koha.t passed.
Signed-off-by: Mason James <mtj@kohaaloha.com>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>