xxxxx.xxxxx.adgroup.add
        ===================================
        创建一个推广组

def add(self, campaign_id, item_id, default_price, title, img_url, nick=None):
        '''xxxxx.xxxxx.adgroup.add
        ===================================
        创建一个推广组'''
        request = TOPRequest('xxxxx.xxxxx.adgroup.add')
        request['campaign_id'] = campaign_id
        request['item_id'] = item_id
        request['default_price'] = default_price
        request['title'] = title
        request['img_url'] = img_url
        if nick!=None: request['nick'] = nick
        self.create(self.execute(request), fields=['success','result','success','result_code','result_message'], models={'result':ADGroup})
        return self.result