Get the participant with the given id.

def get_participant(participant_id):
    """Get the participant with the given id."""
    try:
        ppt = models.Participant.query.filter_by(id=participant_id).one()
    except NoResultFound:
        return error_response(
            error_type="/participant GET: no participant found",
            status=403)

    # return the data
    return success_response(field="participant",
                            data=ppt.__json__(),
                            request_type="participant get")