Django 4.0.0 compatibility

[tswfi]

Change deprecated and removed methods in Django 4.0

• url => re_path
• smart_text => smart_str
• is_safe_url => url_has_allowed_host_and_scheme
• force_text => force_str
• ungettext => ngettext
• urlquote => quote (urllib.parse)

Fix Signals init

Add pytz to requirements. Should migrate from pytz to zoneinfo at some point

Still a WIP. There are few tests that fail with 4.0 but I want to see what happens with the CI and if there are other things that might require attention.

Also gets the filebrowser_safe from my branch that is already 4.0 compatible TODO: this must be switched back as soon as upstream has merged my patch. Also should probably get the package from pypi not from the master branch in git.

Fixes: #2008 and #2007

[tswfi]

https://github.com/stephenmcd/mezzanine/blob/a2fa5c8d96ac6e0a724d214135c5581cae1c8b52/.github/workflows/main.yml#L91 should probably be removed from the on push / pr and another "deploy" workflow be implemented for just the master branch?

[jerivas]

Great work @tswfi!

[github-actions[bot]]

:tada: This PR is included in version 5.1.0 :tada:

The release is available on:

• GitHub release
• v5.1.0

Your semantic-release bot :package::rocket: