add a replace function for std::string
simplify and clarify option parsing
plotSF: also save png
update input to Sep_23, output to Sep_24
avoid empty histos, set two different markers
only compare a subset of the histograms
PowhegPythia8_ZZllnunu: bugfix l4->ll
sync with the datasets Matt is usin for the fakes

Details:
- add SingleTopSChanW (108343, 108344, 108345)
- add singletop_tchan (117360, 117361, 117362)
- add Sherpa_CT10_VVtollqq (157814, 157815, 157816)
- remove Sherpa_VV_lep (126892, 126893, 161963, 174834)
- remove Sherpa_CT10_llgamma (145161, 145162, 126854),
    keep Sherpa_CT10_lvgamma
- remove Sherpa_VV_lep (126892, 126893, 161963, 174834)