Adds dark mode

[der-On]

This adds a fully working dark mode with a dark mode toggle button in the account drop down menu and user preferences form. The dark mode settings is stored in backend user preferences.

This PR also updates to tailwind 3.2

CSS for setting dark mode was taken from https://github.com/WebVPF/wn-darkbackend-plugin

[LukeTowers]

I made some tweaks to the switching themes logic / interface:

@der-On @webvpf this is looking great so far, there's just a few things that need to be fixed before we can get this merged and live for everyone :)

• [ ] Black border on account dropdown in light mode:
• [ ] Ugly borders on dashboard widgets in dark mode:
• [ ] Blue menu item text color in dark mode:
• [ ] Insufficient contrast on buttons and lists in dark mode:
• [ ] Very broken styles on fancy layouts, see the Records form page on the Winter.Test plugin for testing

Black border on account dropdown in light mode:

Ugly borders on dashboard widgets in dark mode:

Blue menu item text color in dark mode:

Insufficient contrast on buttons and lists in dark mode:

Very broken styles on fancy layouts, see the Records form page on the Winter.Test plugin for testing

[LukeTowers]

@der-On could you post the screenshots of the previously identified problematic areas now that you've fixed them?

[der-On]

[LukeTowers]

@der-On I merged in some other fixes from #24, can you resolve the conflicts and recompile? Other than that it looks great! I'm excited to get this merged once the conflicts are resolved.

[der-On]

@LukeTowers Done!