BUG8446: Adds Shibboleth authentication

BUG8446: Adds Shibboleth authentication

 - Use the shibbolethAuthentication syspref to enable Shibboleth authentication
 - Configure the shibbolethLoginAttribute to specify which shibboleth user
   attribute matches the koha login
 - Make sure the OPACBaseURL is correctly set

BUG8446, Follow-up: Adds Shibboleth authentication

 - Fix logout bug: shibboleth logout now occurs only when
   the session is a shibboleth one.
 - Do some refactoring: getting shibboleth username is now
   done in C4::Auth_with_Shibboleth.pm (get_login_shib function)

BUG8446, Follow-up: Adds Shibboleth authentication

 - Adds redirect to opac after logout

BUG8446, Follow-up: Adds Shibboleth authentication

 - Shibboleth is not compatible with basic http authentication
   in C4/Auth.pm. This patch fixes that.

BUG8446, Follow-up: Adds Shibboleth authentication

 - Use ENV{'SERVER_NAME'} instead of syspref OpacBaseURL in order to work with
   multiple vhosts.

BUG8446, Follow-up: Adds Shibboleth authentication

 - Adds missing protocol for $ENV{'SERVER_NAME'}

Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Jesse Weaver <pianohacker@gmail.com>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Tested with the feide idp.
- LDAP login and logout are working
- local login/logout are still working
- CAS login/logout are still working

Instructions for setup can be found on the wiki:
http://wiki.koha-community.org/wiki/Shibboleth_Configuration

Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>