Bug 34889: Convert PatronSelfRegistrationAdditionalInstructions system preference...

Bug 34889: Convert PatronSelfRegistrationAdditionalInstructions system preference to HTML customization

This patch moves the PatronSelfRegistrationAdditionalInstructions system
preference into HTML customizations, making it possible to have
language- and library-specific content.

To test you should have some content in the
PatronSelfRegistrationAdditionalInstructions system preference before
applying the patch. Apply the patch and run the database update process.

 - In the staff client, go to Tools -> HTML customizations and verify
   that the content previously in the
   PatronSelfRegistrationAdditionalInstructions preference is
   now stored there.
 - The HTML customization entry form should offer
   PatronSelfRegistrationAdditionalInstructions as a choice under
   "Display location."
 - Go to Administration -> System preferences and enable
   "PatronSelfRegistration." Set "PatronSelfRegistrationVerifyByEmail"
   to "Don't require."
 - Go to the OPAC and click "Register here."
 - Submit a new registration and confirm that the content that was
   previously stored in the system preference is shown correctly on the
   registration confirmation page.
 - Update and reinstall active translations (for instance fr-FR):
   - cd misc/translator/
   - perl translate update fr-FR
   - perl translate install fr-FR
 - Enable the translation if necessary under Administration -> System
   preferences -> language.
 - Enable the "opaclanguagesdisplay" preference if necessary.
 - Edit the PatronSelfRegistrationAdditionalInstructions HTML
   customization and add unique content to the "fr-FR" tab.
 - Go to the OPAC and switch to your updated translation.
   Complete the online registration process again to confirm that the
   content you added for your translation shows up correctly on the
   confirmation page.
 - Go to Administration -> System preferences and confirm that the
   PatronSelfRegistrationAdditionalInstructions  preference has been
   removed.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>