Esg/alkaline

[ZackTully]

This pull request is ready to merge. Tests pass.

Feature or improvement description

This pull request makes two big changes.

1. Alkaline model from @elenya-grant. Previously, electrolyzer.cell.py contained all of the PEM electrochemical calculations. Now, electrolyzer.cell.py has been replaced with electrolyzer.PEM_cell.py and electrolyzer.alkaline_cell.py to allow for either PEM or alkaline electrolyzer modeling.
2. New modeling schema. To separate the PEM and alkaline behavior and allow for the additional alkaline inputs, the modeling schema has been reorganized. The modeling schema is now organized to match the structure of the code better by grouping model parameters according the class they are used in (i.e. `supervisor', 'stack', 'lcoh', etc.).

Impacted areas of the software

Almost everything is impacted by this pull request. With the new modeling schema, reading inputs for the initialization of supervisor, stack, and cell are different.

Additional supporting information

Next Steps Create alkaline-specific tests for alkaline_cell.py and alkaline functionality in stack.py and supervisor.py.

[camirmas]

@ZackTully it's looking good. I'm not familiar with the alkaline modeling specifics so maybe @elenya-grant or @nRiccobo should take a look too