initial classes and workflow

I am creating this as a draft for a place for feedback/discussion.

This is how I envision the classes for the shift/openmc integration. Initially my thought was to have the OpenMC and Shift classes inherit from the MCSim class, but as I started working through the requirements (at least on the openmc side) for setting up the run information, I think it might make more sense to have 3 separate classes, but OpenMC and Shift need the user object as input. I am open to discussion (probably on a call) on how to structure this to be most effective.

What I have in here so far is the flow and a bit of the envisioned modularity. I also do the initial check for whether or not to run each code in the precheck.