add closure test to n3fit
Created by: wilsonmr
I wanted to seperate out the closure test changes from other changes so creating a new PR
This closure test adds the ability to closure test with n3fit:
- leverages use_fitcommondata during fit
- changes fit function name to avoid conflict with fit resource
- parses fit as a filtered runcard directory in same location and with same name as the runcard
- uses 'old' technology for actually producing pseudodata
- adds logic for whether or not to gen mc replicas