Bug 29948: (follow-up) Update system preference description and heading

Bug 29948: (follow-up) Update system preference description and heading

This follow-up:
1. Updates the OPACAuthorIdentifiersAndInformation system preference
   description.
2. Changes the OPAC heading used on the bibliographic record and
   authority record detail pages from "Author identifiers/information"
   to "Author information". Identfiers are a subset of author information
   and having just "Author information" is sufficient. In addition,
   the authority record doesn't have to include identifiers.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>