Jet systematics (v1)
Should address #4 (closed) , but with a few loose ends remaining:
- propagating jet variations into MET and MET covariance/significance
- more testing and validation
- copying and patching some files from CMSSW isn't integrated with setuptools yet
- the NanoAODv4 file in the tests isn't reachable for the CI, so the tests will fail for now
- probably more - feel free to report
Anyway, I'd like to declare beta one of these days, and I really want this in for that (as one of the most tricky things that must be supported), so unless there are objections I'll merge this soon-ish, and we can fix the remaining issues later on.