Concentric Pie Charts need multiple labels

[jonwinstanley]

I think concentric pie charts need the ability to add multiple sets of labels.

I fixed myself by simply adding the following to the gConcentricPieChart class

public function addLabel($labels)
{
    $this->setProperty('chl', urlencode($this->encodeData($this->getApplicableLabels($labels),"|")), true);
}