Further cleanup, paying technical debt, ...

[LukasKalbertodt]

In #996 I did a huge cleanup of the whole project. There wasn't enough time to do everything I could think of, so this issue is a list of things that can (and often should, IMO) still be improved in the near future.

Consistency

• Use arrow functions for all components
• Sort all imports (one block for externals, one for internals)
• Convert // comments to propery /** */ doc comments where appropriate

Deployments

• Use proper GitHub deployments ("environments") so that it's easy to see in a PR that it's deployed. Like with Tobira.
• Delete old test deployments automatically?

Other stuff

• Enable noImplicitAny in typescript (roughly 60 errors still)
• Check usage of deprecated APIs
• Improve eslint config by using shared one (will do so soon)
• Add better tests (maybe only after the redesign?)
• Switch to React createRoot for proper React 18 mode
• Replace react-hotkeys (unmaintained & breaks React 18)
  • https://github.com/JohannesKlauss/react-hotkeys-hook
  • https://github.com/jamiebuilds/tinykeys
• Maybe eject from CRA
  • That would allow us to get rid of JSX annotations in all files, see Let jsxImportSource be configurable through tsconfig.json facebook/create-react-app#9847