Bug 12636: Do not display unique patron attributes in the batch patron modification

Bug 12636: Do not display unique patron attributes in the batch patron modification

Batch patron modification should not offer to update patron attributes
with values which are designated as unique since such attributes are
required to be unique to a single patron.

Test plan:
Create some patron attributes, some should be unique.
Use the batch patron modification tool to modify patrons.
With this patch, the patron attributes marked as unique won't be
display anymore.

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Brendan Gallagher brendan@bywatersolutions.com