Bug 10796: Handle can_change_password on the staff interface

Bug 10796: Handle can_change_password on the staff interface

This patch makes the staff interface handle the new flag when editing
the categories. I didn't add the flag to the list of categories table
because it makes it too big, but can be easily added if required by
users or QA.

To test:
- Along with other patches from this bug, edit patron categories
=> SUCCESS: Notice the changes are correctly stored
- Sign off :-D

Signed-off-by: Liz Rea <wizzyrea@gmail.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>