Fix ordering option for the barChart.

Fix the bug: ordering not working on barChart.

If you write in the barChart definition:

1. **chart.ordering(function (d) { return  d.data.value;   });** 
It will order the barChart xAxis by value increasing.

2. **chart.ordering(function (d) { return  -d.data.value;   });** 
It will order the barChart xAxis by value decreasing.

3. **chart.ordering(function (d) { return  d.data.key;   });** 
It will order the barChart xAxis by key, alphabetical order.




This is not quite right because it only sorts the first stack. If there are multiple stacks, the latter stacks will get tacked on unsorted, and ruin the order. Probably we need to flatten first, then sort.