Bug 34869: Convert OPACResultsSidebar system preference to HTML customization

Bug 34869: Convert OPACResultsSidebar system preference to HTML customization

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

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

 - Go to the OPAC and perform a catalog search.
 - Confirm that the content in the sidebar under the search facets,
   which was previously in the OPACResultsSidebar system preference, is
   still displayed.
 - In the staff client, go to Tools -> HTML customizations and verify
   that the content from OPACResultsSidebar is now stored there.
 - The HTML customization entry form should offer OPACResultsSidebar as
   a choice under "Display location."
 - 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 OPACResultsSidebar HTML customization and add unique content
   to the "fr-FR" tab.
 - Go to the OPAC and switch to your updated translation. Perform
   another catalog search to confirm that the content you added for your
   translation shows up correctly.
 - Go to Administration -> System preferences and confirm that the
   OPACResultsSidebar 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>