Bug 23420: Add OPACSuggestionUnwantedFields system pref

Bug 23420: Add OPACSuggestionUnwantedFields system pref

To test:
-Apply patch
-Check OPACSuggestionUnwantedFields
-Check some fields as unwanted
-Go to the OPAC suggestion page and make sure these correct fields are hidden
-Turn on the system preference AllowPurchaseSuggestionBranchChoice to see the branch choice on the form
-Make sure you can correctly hide this one and still submit the purchase suggestion for without error.
-Go through each option and make sure it hides properly.

Note: You will only see the patron reason field when there are authorised values in the OPAC_SUG category

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>