Bug 29230: Add Koha::Patron->messages

Bug 29230: Add Koha::Patron->messages

Add methods to return the messages attached to a patron.

It will add the capability to access them from notice templates.

Test plan:
Define some messages for a given patron
Go to the circulation page of the patron and confirm that they are still
displayed

Test the notice templates:
Add to HOLD_SLIP the following content
"""
[% SET messages = borrower.messages %]
[% IF messages.count %]
Messages:
<ul>
  [% FOR m IN messages.search( message_type => 'L' ) %]
    <li>[% m.message %]</li>
  [% END %]
</ul>
[% END %]
"""

To display all the messages from staff ('L')

Adapt following your needs.

Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>
Signed-off-by: Stina Hallin <stina.hallin@ub.lu.se>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>