Creates a new dataset instance for this scene.
        
        :param      dataset | <XChartDataset>
        
        :return     <XChartDatasetItem>

def addDataset(self, dataset):
        """
        Creates a new dataset instance for this scene.
        
        :param      dataset | <XChartDataset>
        
        :return     <XChartDatasetItem>
        """
        item = XChartDatasetItem()
        self.addItem(item)
        item.setDataset(dataset)
        return item