Separating Rewrite GT String and PU input

[AdrianoDee]

At the moment we have only one entry we can use to specify both the (recycling) input dataset and the pileup input to be fetched (Rewrite GT String). This is limiting the possibility to specify two different targets and makes things a bit clunky. I would that input parameter in two. E.g. Pile-up Input and Recycling Input.