Bug 9756 - Patron self registration missing preference PatronSelfRegistrationAddition...

Bug 9756 - Patron self registration missing preference PatronSelfRegistrationAdditionalInstructions

The patron self registration system references a system preference
PatronSelfRegistrationAdditionalInstructions as a free text field
to add additional instructions for newly self registered patrons,
but the system preference in neither created in the database,
nor exposed via the staff interface.

Test Plan:
1) Apply patch
2) Run updatedatabase.pl
3) Add some text to the new system preference
   PatronSelfRegistrationAdditionalInstructions
4) Enable opac self registrations and complete a self registration
5) Note the additional instructions you entered appear on the
   "registration complete" page

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Jonathan Druart <jonathan.druart@biblibre.com>
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>