Add ECO version of desal

[johnjasa]

Add ECO version of desal

H2I includes a desal model.
GreenHEART used to include another option called desal_model_eco.py.
Noted here: #384 (comment)

Proposed solution

It's unclear to me if we need both desal models because I haven't looked into the differences.
If it makes sense to bring this desal model into the new framework, then that is the solution here.

Alternatives considered

Additional context