Merge the fedmsg notifications on commit logic into the default hook
    
    This way we can finally split the web-hooks notifications from the fedmsg
    ones while not duplicating the entire logic around how to build the
    payload sent.
    
    Fixes https://pagure.io/pagure/issue/2413
    
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>