Prevent JavaScript error on non-Novelist sites

Unless the Evergreen site in question is signed up and configured to
support Novelist added content, every details page will generate a
JavaScript error due to the reference to an undefined JavaScript
function. Guard against that by testing for the presence of the Novelist
URL.

Signed-off-by: Dan Scott <dscott@laurentian.ca>
Signed-off-by: Ben Shum <bshum@biblio.org>