Bug 12670: Show materials label instead of code

 Bug 12670: Show materials label instead of code

In catalogue/detail.pl, if items.materials is linked to an authorised
values list, show label instead of code.

Test plan:
1/ Create an authorised values list 'MATERIALS' with some values
2/ In default MARC biblio framework, link an item subfield to
'items.materials', and to the AV list 'MATERIALS'
3/ Edit an item and give a value for this subfield
4/ Go to biblio record detail page (catalogue/detail.pl)
5/ In the items table, the authorised value label should be displayed.

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>