Use extensions template from NSS
    
    Drop certmonger's custom extension template and use the sequence of X509v3
    extensions template from NSS.
    
    The certmonger template had a bug that caused certmonger to create CSRs
    with invalid DER. It was encoding extension's critical element even for
    default value FALSE.
    
    Fixes: https://pagure.io/certmonger/issue/223
    Signed-off-by: Christian Heimes <cheimes@redhat.com>