`CategoryChart.addSeries` could support additional call signature for interoperability with Scala

[vreuter]

I hit a case where the arguments that I'd like to pass to addSeries won't jointly "fit" in any combination of the slots provided by the current signatures of addSeries for a CategoryChart.

I'm working in Scala and had been using .toArray to conversion scala.collection.immutable.List to the equivalent of int[], but now I want to lift the restriction of having my x-value type be Int. Naïvely, I thought that that signature of addSeries which accepts two lists would work, but I'd overlooked that the y-value collection element type must be a subtype of java.lang.Number.

It would be nice in such a case if the client code didn't need to cast each element, and could instead use a signature which supports something like List<?> as the x-value type, and int[] or double[] still as the y-value types.