Bug 19160: CAS Single logout

Bug 19160: CAS Single logout

CAS supports single logout, where if you logout of one application it
logs you out of all of them.

This bug implements this

You will need a CAS server (with single logout configure),
and at least 2 applications (one being Koha)

1/ In Koha login via CAS
2/ Login to the other application via CAS
3/ Logout of the other application
4/ Notice you are still logged into Koha
5/ Log out of Koha
6/ Apply patch
7/ Login to Koha via CAS, login to other app via CAS
8/ Log out of other app
9/ Notice you are logged out of Koha

If you dont have CAS, this patch should be a no op, you could test that
1/ Login and logout normally
2/ Apply patch
3/ Login and logout still work fine

Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Patch works as described, local login still works correctly.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>