creates an element tree representation of an empty PAULA XML file.

def gen_paula_etree(paula_id):
    """
    creates an element tree representation of an empty PAULA XML file.
    """
    E = ElementMaker(nsmap=NSMAP)
    tree = E('paula', version='1.1')
    tree.append(E('header', paula_id=paula_id))
    return E, tree