Cleanup backend and add settings API

[evan10s]

• Add simple way to persist and retrieve settings that aren't environment variables
  • We store settings in settings/settings.json
  • Env vars might technically get the job done, but people adjusting them may have to check multiple locations (README, code, etc.) to understand them, and immediate validation is unavailable.
  • Current settings values can be retrieved all at once using an API endpoint (GET /api/v1/settings)
  • An individual setting value and be updated as well: (POST /api/v1/settings/:name with JSON body { "value": "string" }). The required format is enforced by the express-validator package; I removed the jet-validator library included with the TypeScript template because it output extremely vague error messages

I also removed the remaining cruft from the TypeScript/Express template I use, including all references to users and authentication, and simplified/clarified naming/comments in a number of other spots.

Closes #4

[github-actions[bot]]

:tada: This PR is included in version 1.0.0 :tada:

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• v1.0.0

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