Decouple UI state from workflow state

Currently, our models' `get/set_model_state` methods follow the format of aiida-quantumespresso, rather than that of the app. Best we update these to follow the UI format, converting to workflow format at submission.

For example, smearing choices in the UI aren't saved unless the user also selects a metallic state. Another is the shape of the eigenvalues in the Hubbard model (UI different from workflow inputs), for which we have to parse both ways. These sort of things should only happen at the workflow level.

Need to think carefully w.r.t backwards compatibility.

Pinging @superstar54