webui: handle back button when unauthenticated
    
    using browser history when unauthenticated causes transition to
    the original and/or preceding facets. But nothing works since
    all commands fail due to expired credentials in session.
    
    These changes make sure that user stays on login screen if he misses
    valid session credentials while he wants to switch to facet which
    requires authentication.
    
    https://fedorahosted.org/freeipa/ticket/4353
    
    Reviewed-By: Endi Sukma Dewata <edewata@redhat.com>