[Umbrella/RFC] Improvements to the scheduler & platforms layer

[berekuk]

So I took a closer look at how backend/platforms are implemented, and I have a few ideas on how to improve.

@NunoSempere, let me know if you're ok with all these or if you have other suggestions.

• [x] Separate fetching and storing layers more clearly (see #34)
• [x] CLI with names instead of numbers (current approach seems quite fragile to me)
• [ ] #9
• [x] Unify platforms list on frontend and backend (will require figuring out how to avoid bringing backend platforms code to the frontend bundle, but I think it's doable with lazy loading or some other trick)
• [ ] #35
• [ ] Support incremental updates, as I mentioned in PS in my https://github.com/QURIresearch/metaforecast/issues/30#issuecomment-1081319952 comment

This is a longer term roadmap, and the last two items are a bit more complex, but I believe that they're quite beneficial. Getting closer to the "metaforecast data is never stale" goal would be great.

[NunoSempere]

Most of these sound good, no strong opinions on unifying the platforms list.

[berekuk]

One more thing: I'd like to change the platform field values in the DB and other related code (e.g. stars.ts) to the short platform name/id, e.g. "goodjudgment" instead of "Good Judgment", and leave longer titles just for displaying. This is useful for consistency, for type safety, etc.

(from https://github.com/QURIresearch/metaforecast/issues/33#issuecomment-1084570512, but relevant here too)

I also think that stars.ts code maybe should be split and moved into platforms files too. I see the benefit of having it all in a single file, but I don't like the fragility of "if I make a typo in a platform's name then it'll just fallback on 2 stars default without any signal that something went wrong".