Update dependencies && remove unused vars

[chinatsu]

pretty huge pr here, but i promise that all i've done is

1. update dependencies (i used npx npm-check-updates --interactive --format group to check)
2. fix backwards incompatible changes with the react-markdown dependency
3. go through the compiler warnings and remove all instances of no-unused-vars, and some other eslint issues.
   • i have not verified that everything works as intended, but i don't think we'll need to do that either. we'll create new tasks if we see something bad as a result of this, maybe? :)
4. circumvent a problem regarding source maps and create-react-app.
   • the solution is basically to ignore the warnings due to the unmaintained state of create-react-app, we cannot fix it properly.
5. replace a couple of dependencies that have not been updated in many years.
   • there were replacement libraries which i could use to almost fully drop in without much changes.

i did set out to solve all of the npm i issues, but it's not possible. the dependencies that baseui pull in do not support react 18, so in order to fix those problems we'll have to toss out all of baseui.

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so generally what i've learned is, if we want to use react 18:

• baseui shouldn't be used
• create-react-app shouldn't be used

both of these points involve some difficult choices and potentially lots of work.

[JeremiahUy]

lgtm, kjørte branchen lokalt og for å dobbel sjekk :)