Refactor Partner Site Unit Form

[YazeedLoonat]

I think the current unit form validation has been letting things through the cracks. A few times we've ran into issues where somehow a unit has an ami percentage that its ami chart doesn't support. Or that the ami chart overrides weren't taken properly or weren't reset properly

I think if we take the time to refactor that form we could save ourselves some heart ache.

It may also be a good space to add a validation endpoint in the API to maybe help with validation?