Systematics and weights

[areinsvo]

I wanted to make a GH issue to keep track of the systematic uncertainties and remaining weights we need to implement.

Missing weights:
NNLO scale factors for W+ets, Z+jets, and G+jets <- take from Michael/monotop
POG-provided ID scale factors
Trigger scale factors <- monojet seems to have finished most of these studies

Shape systematics
EWK NLO, QCD NLO, ad-hoc NLO corrections from Andreas
NNLO scale factors
JEC/JER
b-tagging scale factors

Rate systematics
Luminosity
tau veto
Theory uncertainties: pdf, cross section
DeepAK15 scale factors
Soft drop mass correction
Object ID scale factors
Trigger scale factors
QCD normalization