ENH: 3525 - Link to OPAC View from Staff Bib

ENH: 3525 - Link to OPAC View from Staff Bib

This patch adds a link to the OPAC view for a bib
record from the staff client so catalogers can
preview changes as the patrons see them.

This patch only shows the link is the OPACBaseURL
system preference has a value.

[RM note re bug 2152: this is probably enough to keep
 OPACBaseURL after all - the staff interface has
 no other way of reliably knowing where the OPAC
 is.]

Signed-off-by: Galen Charlton <gmcharlt@gmail.com>