Recipes plus Django 4 support

[MrCordeiro]

This addresses #382 and #403

• Add support for Django 4.0
• Fixed a typo on the fixtures
• Add "Recipes" section with an example on how to translate a custom main menu i18n

Some caveats:

• I was unable to upgrade tox since Wagtail 2.15 has a Django <3.3 dependencies.

When that was solved, ideally we would want to drop support from Wagtail <2.11 and Django <2.2 since they are no longer supported.

[JeffKnorr]

I also needed to make these changes to use with Django 4. This update looks good to me--for what that's worth from some random guy on the Internet. :)

[justinsg]

Django 4 support in the PR is not complete - need to remove usage of django.conf.urls.url which was deprecated in Django 3.1 and now removed in Django 4.0.

#414 does provide working Django 4 support, so perhaps reduce this PR to the recipe/docs changes only?

[MrCordeiro]

Hi @justinsg, I'm waiting for #409 to be resolved before doing any further work on this PR.

That being said, there were new ideas on issue #74 that may even allow for simpler versions of the recipes added here, so I converted this PR to a draft.

[MrCordeiro]

I merged #414, so I'll be abandoning this PR.