Sort dataset diffs

Created by: felixhekhorn

Can we please sort Dataset differences and cuts? with whatever unique sort you like - e.g. alphabetic ... else I can only guess by the length that this is the same as in this report

I guess it should be somewhere here: https://github.com/NNPDF/nnpdf/blob/ce6c05cacec95dee36c577503c9a1109daa2908a/validphys2/src/validphys/fitdata.py#L296