Bug 22061: Public route to change password

Bug 22061: Public route to change password

This patch implements a route to change patron's password for
unprivileged users. It's intended for using in the OPAC (or however
consumers find it useful).

It is a starting point for the public API, and the bug also implements
the on/off switch some community members asked for.

To test:
- Apply this patches
- Run:
  $ kshell
 k$ prove t/db_dependent/api/v1/patrons_password.t \
          t/db_dependent/api/v1/auth.t
=> SUCCESS: Tests pass! i.e.
        - RESTPublicAPI is honoured
        - The /public/patrons/:patron_id/password endpoint works as
        expected
- Use your favourite API testing tool to try the endpoint.
- Sign off :-D

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>