Draft: style: adopt Airbnb lint rules

Closes #275 (closed)

Strategy

1. Enable Airbnb lint rules
2. Run eslint auto fix on all files npm run lint:fix
3. For all the remaining error, convert the error into a warning via package.json
4. (later: When changing components, try to fix the warnings)

Because warnings are always displayed by Create react app, I disabled eslint DISABLE_ESLINT_PLUGIN here (there are too many warnings to be helpful). I think this doesn't really have much consequences, as errors are still displayed in the browser. To get all errors without warnings, I added the command: npm run lint:quiet.

For now, I just converted all rules resulting in errors to warnings. In case we decide a certain rule is not helpful, we can disable it all together.

It will be easier to merge this once (most of) the open MRs are merged