Bug 27454: Add sorting of patron attributes

Bug 27454: Add sorting of patron attributes

This patch adds sorting on class code for the patrons attributes forms
on the memberentry page.

Test plan
1) Create a couple of different patron attributes
2) Go to the patron add page
3) Note the order in which the patron attributes load at the bottom of
   the page.
4) Reload the page and note the order of those attribues may change (if
   it doesn't, try reloading again.. it's random)
5) Apply the patch
6) Reload the page a few times and confirm the attributes are now
   ordered.
7) Signoff

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>