Incorporate cross sections and luminosity into event weights
Include into event weights cross sections and the integrated luminosity. As a result, no further rescaling of simulation is needed, and it's eliminated from the many places in the repository where it was reimplemented.
I ran steps 0 to 3 of launchAnalysis.sh using the nominal (data-driven) analysis and without systematic variations. I checked the final mT distributions, and the normalizations of data and simulation in those plots agree, which validates the change.
This MR depends on !44 (merged) (in fact, it has been rebased on the corresponding branch) and should be merged after that one.