Bug 8952: Add http:// to url in social media links on opac-detail

Bug 8952: Add http:// to url in social media links on opac-detail

This patch adds a variable to the template, "protocol" based on
whether "using_https" is set. The appropriate protocol is
inserted before social media links.

To test, confirm that  OPACBaseURL is set and lacks "http(s)://"
Social media links should include correct URLs.

A follow-up patch could copy use of this [% protocol %] variable
in other parts of this template which duplicate large chunks of
HTML based on [% using_https %].

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>