Copy details link to Evergreen library page by default

Copy details link to Evergreen library page by default

Add a new library setting, 'lib.prefer_external_url', to force library names in
copy details pages to link to their associated 'lib.info_url' setting rather
than the Evergreen-generated page. In the absence of a 'lib.info_url' setting,
the name will fall back to being linked to the Evergreen-generated page.

Per discussion with Ben Shum and Kathy Lussier.

Signed-off-by: Dan Scott <dscott@laurentian.ca>
Signed-off-by: Dan Wells <dbw2@calvin.edu>