BUG8446, Follow up: Adds Shibboleth authentication

BUG8446, Follow up: Adds Shibboleth authentication

- Use syspref OpacBaseURL instead of ENV{'SERVER_NAME'} as this wont
  work if koha is behind a reverse proxy.
  - To use multiple vhosts, set OpacBaseURL per vhost explicitly with
    'SetEnv OpacBaseURL Value' as per Bug 10325

BUG8446, Follow up: Adds Shibboleth authentication

- Ensure user is returned to requested page after authentication
  - Added querystring to the target path in shibboleth URL so
    that when a user is authenticated he/she is returned to the
    correct page they requested before authentication.
    Example where this is important: When a user clicks a direct
    biblio link of the form - /opac-detail.pl?biblionumber=12345

BUG8446, Follow up: Remove unused imports from scripts

- Remove import of deprecated C4::Utils module from shibboleth
  authentication module: Auth_with_shibboleth.pm

Signed-off-by: Jesse Weaver <pianohacker@gmail.com>
Signed-off-by: Matthias Meusburger <matthias.meusburger@biblibre.com>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>