Merge 2x2_sim repo into ND_Production -- one repo for ND production

[mdolce8]

We should really consider at this stage to merge together the ND_Production and 2x2_sim repo together. Generating a production sample is starting to get a little messy, in that the codes for each process are starting to appear in different places, e.g.: the run-tms-reco stage is inside ND_Production, while the other stages are in 2x2_sim. This actually makes sense, since 2x2_sim was originally designed for 2x2 only, but now that we have so many of the production steps fleshed out, this is a good time to consider having a single repository for all stages of a ND production sample.

From the considerations of the ND Prototypes & ND Reco/Sim Workshop, here are a few things we definitely want. I am sure that more essentials may appear as more steps of production become solidified:

• maintain the commit history of 2x2_sim
• ensure the workflow is still sensible for a 2x2 sample only -- and not have the other elements of the ND (like TMS) interfere with generating a 2x2 production sample.