[frogend] Settings refactor

[f0x52]

Progress towards refactoring the settings interface, almost finished now.
The codebase has grown kind of organically over time, writing newer/better ways to do things but not reflecting them in the existing sections. Most importantly this includes the use of RTK Query, and various refactors of the form field structure I yakshaved.

I'm standardizing on RTK Query everywhere, and self-designed form api/components that have a flexible hook structure to hold their data so they can be used in specialized usecases, or with a set of standardized form components in various types usage.

Goals:

• Refactor internal API structure + form fields
  • Authentication
  • User profile
  • User settings
  • Admin settings
  • Admin actions (media cleanup)
  • Admin federation (overview, detail page)
  • Admin federation (bulk import/export)
  • Admin custom emoji (overview, detail, steal-this-look)
• Remove lib/api completely, components/form-fields.jsx, old Redux reducers

NLnet Milestone 16: Settings interface refactor

[tsmethurst]

Love how this is coming along, it looks a lot neater and easier to reason about!

[tsmethurst]

oh mannnnnn it's coming along, i'm excited 👀

[f0x52]

All main goals are finished now, will review the CSS tomorrow and it can use some more testing!

[f0x52]

fixes #1253

[tsmethurst]

Phew! Okay, it looks good! I have some comments as you can see, but they're mostly like 'nice' and small questions. I don't see anything here that gave me pause. Great work f0x! Feel free to merge it whenever you're ready :)