Non-intrusive ROM interface

[cwentland0]

Need to add a general class interface for non-intrusive ROMs. This can be further broken down into those which still need a time integrator and those which do not. This will presumably require adding a dummy explicit time integrator that just acts to advance the solution from step to step.

I think that David Xu's TCN-CAE, Elizabeth Qian's Lift & Learn, and Romit Maulik's CAE-LSTM are good candidates to implement first and suss out a modular framework.