Feat custom email icons

[HenryRoutson]

What kind of change does this PR introduce?

Allowing no or custom prefix icons / widgets

What is the current behavior?

Prefix icons are set

What is the new behavior?

Prefix icons can be removed or changed

Additional context

I would have put an issue, but this was almost quicker.
The reason for the pull request is simply that the design i want to create doesn't have icons.

I also made a small simplification with the navigateHome function

Thanks!

[HenryRoutson]

This is the sort of design i'm looking to create

[HenryRoutson]

I've added a minimal dark mode example,
as it more closely matches the supabase react auth ui with this merge.
I think an example for applying themes would be good in general.
https://docs-git-docs-add-next-js-server-component-docs-supabase.vercel.app/docs/guides/auth/auth-helpers/auth-ui

[dshukertjr]

Thanks for such an amazing PR! I love it! It looks very nice!

[dshukertjr]

Would you be able to update the variable names on the places that they are referenced?

[HenryRoutson]

Yep, done

[dshukertjr]

Thanks for this PR!