Add "order" to stacked charts

[triplem]

In VEGA Lite there is the notion of ordering for stacked charts. Right now, the only possibility to sort is by the color-field (stack grouping field). But there is no ORDER field for using other fields to order the stack in hanami. It would be great, if this is supported.

https://vega.github.io/vega-lite/docs/stack.html#sorting-stack-order

[jsa-aerial]

sounds good - I have to add / change some other stuff in layering and will add this at the same time.

[jsa-aerial]

I know long time, but I think this is covered in latest release.