Add systematicRedefine methods

The title is a bit of a misnomer as all that has been done so far is systematicStringRedefine().

We figured we'd open a MR here to see if anyone else thinks it might be useful to have systematicRedefine() and systematicStringRedefine(). So far we use it to e.g. select on jet eta and sort jets by pT without having to define additional columns for the output.

If this seems like a good idea we can go and create systematicRedefine().