Bug 27430: Change password minimum value hint when patron category is changed

Bug 27430: Change password minimum value hint when patron category is changed

If patrons category is changed during add or edit password
minimum value doesn't change. This patch adds ajax call to
fix this.

To test:
1. Add password minimum length for patron
categories A and B.
2. Create a new patron with category A.
3. Change patrons category to B.
4. Note that password minimum value doesn't change
on hint text.
5. Apply patch.
6. Repeat patron creation, password minimum value
should now change correctly.

Signed-off-by: Sally <sally.healey@cheshiresharedservices.gov.uk>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>