Bug 34894: Convert OpacSuppressionMessage system preference to HTML customization

Bug 34894: Convert OpacSuppressionMessage system preference to HTML customization

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

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

- In the staff interface, locate a bibliographic record and open it for
  editing.
- Under tab 9, tag 942, change subfield n, "Suppress in OPAC", to "Yes"
  and save the record.

- Go to the OPAC and try to navigate directly to the bibliographic
  detail page for that record:
  /cgi-bin/koha/opac-detail.pl?biblionumber=X
- You should be redirectd to the "Blocked" page. Under the message "You
  are not authorized to view this record" you should see the content
  which was previously in the OpacSuppressionMessage system preference.

- In the staff client, go to Tools -> HTML customizations and verify
  that the content from OpacSuppressionMessage is now stored there.
- The HTML customization entry form should offer OpacSuppressionMessage
  as a choice under "Display location."
- Update and reinstall active translations (for instance fr-FR):
  - perl misc/translator/translate update fr-FR
  - perl misc/translator/translate install fr-FR
- Enable the translation if necessary under Administration -> System
  preferences -> language.
- Enable the "opaclanguagesdisplay" preference if necessary.
- Edit the OpacSuppressionMessage HTML customization and add unique
  content to the "fr-FR" tab.

- Go to the OPAC and switch to your updated translation. Try to view
  the suppressed record again and confirm that the content you added
  for your translation shows up correctly.
- Go to Administration -> System preferences and search for
  "OpacSuppression." The description of these preferences should show an
  updated message about using HTML customizations to create
  OpacSuppressionMessage content.

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>