Bug 3702 add branch description as primary sort for items in staff mode

Bug 3702 add branch description as primary sort for items in staff mode

The default sort order for items attached to a title in staff mode is
items.dateaccessioned desc.  This means that a particular library's holdings
will be scattered through the list -- a special problem when it comes to serial
issues.  I've done a change to Items.pm that makes the sort order branch
description followed by dateaccessioned.  Thus, a library's holdings will be
grouped together in the display.