Add a 'RUN' wrapper to capture all inputs a level above 'realization'

[jameshalgren]

To make Ngen-based simulations more reproducible, we have been discussing a wrapper and hash system that would track exactly what inputs, configuration, and environment are used for a given canonical simulation using the ngen framework. We propose calling these individual simulations and the associated master configuration file a 'RUN'.

An initial PR with a basic demonstration is in development -- see here for prior effort in this direction.

[jameshalgren]

ping @ZacharyWills

[ZacharyWills]

#17 Here's a good spot for specific code discussion but probably not long-form discussion of the topic which can happen here in the issue.