manager: split get_timed_login_details_for_display into two functions
    
    The function is only ever called in two distinct ways:
    
    1) to check about timed login
    2) to check about automatic login.
    
    Since it's used in completely distinct ways and has somewhat distinct
    implementations for each, split it up into two functions for clarity.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=746492