Add PEM BOP considerations

[johnjasa]

Add PEM BOP considerations

Prior versions of GreenHEART included some PEM balance of plant (BOP) calculations.
These are not included in the framework and the remaining unconnected files were removed in #384.

Proposed solution

If we want to use or include these BOP calculations, we'll need to add them back into the current framework.

Alternatives considered

Additional context