NextJS and other improvements

[berekuk]

Seems like this will to be a typical epic branch with a mix of many big refactorings.

• upgraded: react 18, modern webpack with nextjs, modern redux and some redux-toolkit, etc.
• merged all css in legacyStyles.css (necessary for upgrading since nextjs doesn't allow component-level css imports)
• added some typescript (non-strict and very lenient for now)
• had to replace most of @connect decorators with a more verbose syntax since decorator syntax has changed (react-redux recomments to use hooks these days)
• added prettier

This branch is still unstable and unfinished. I'm unsure which parts are unstable because of existing bugs (e.g. because of #1011) and which parts were broken by the upgrade. I'm still in the process of figuring out how everything works.

Stabilizing this PR is the first priority, but while I'm jumping around the codebase and poking my dev frontend instance, I might do some additional refactorings when it matches the current frontend best practices (e.g. functional components instead of classes), or when the change is safe and local enough.

I promise not to do any significant product-level changes here, though. (Might throw in some minor stuff that's relevant for debugging, e.g. nprogress or better error reporting).

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[Incognito]

I don't maintain this project but... Just a thought: Prettier makes no factual code changes but updates several hundred files, making the meaningful diffs harder for humans to find and read. Could easily be done in stand-alone PR first.

[berekuk]

@Incognito I agree in theory, but in practice this doesn't seem to matter in this specific case:

• prettier commit is separate (8461ac66f4db4e30eae8dc96ea150b23a1944948) so it's still possible to review other changes with git diff from the specific commit hash
• the final diff for this PR will be huge anyway, and tbh I don't expect anyone to have enough time to review it all
• clear separate PRs are nice, but velocity is important too, and there's a ton of work to do here (this project was pretty unmaintained for the last few years), and I'm cutting some corners intentionally, so that this will take a week of my work instead of a month

[OAGr]

@Incognito I just wanted to say, thanks for the comment, and we are really appreciative of suggestions, even when we don't wind up taking action on them. @berekuk ultimately makes calls here.

[berekuk]

Superseded by #1035.