Add an option in client GUI to add the wa=wsignoutcleanup1.0 parameter to the logout confirmation message

[AlistairDoswald]

Currently when logging out from a WS-Resource, keycloak will redirect directly to the client and add no wa parameter. However, from the specification in the appendix C.9, upon logout keycloak should send the wa=wsignoutcleanup1.0 parameter. However, as we cannot garenty will support this message, this should be optional