Add weight name to Pythia8B interface
Add weight name to Pythia8B interface.
This should add weight to P8B_A14NNPDF23LO_pp_JpsimumuZmumu in https://its.cern.ch/jira/browse/AGENE-2104
@ewelina, do you know what is the reason why the Pythia8B interface is so different from Pythia8?