Implement OpenID Connect static clients
    
    This implements static clients, which can be put in a different database
    than the normal OpenID Connect data, so that they can be put into a configuration
    file.
    
    Signed-off-by: Patrick Uiterwijk <puiterwijk@redhat.com>
    Reviewed-by: Pierre-Yves Chibon <pingou@pingoured.fr>
    Reviewed-by: Howard Johnson <merlin@merlinthp.org>