Update flask-babel to 3.0.0

[pyup-bot]

This PR updates Flask-Babel from 0.12.2 to 3.0.0.

Changelog

3.0.0

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Major version bump as this version removes support for Python 3.5 and 3.6, along with multiple
major breaking changes. Hope you've been following SemVer :)

- Dropped support for end-of-life Python 3.5 and 3.6, added tests for 3.10 and 3.11.
- Fixes to documentation to address outdated links and settings (204, 201)
- Jinja version 3 or greater is now required (released 2021)
- Removed Babel._date_formats, use the public Babel.date_formats instead.
- list_translations() always returns the default locale, even if it does not exist. (75)
- Add lazy_npgettext() (68)
- Babel.locale_selector and Babel.timezone_selector no longer exist. They must be provided
either when the Babel() object is created or when init_app() is called. This is to support
having a single Babel object for multiple Flask apps (107) as well as to simplify settings
and multi-threaded state.
- Most configuration options can be passed directly through init_app().

2.0.0

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Starting with version 2, flask-babel drops official support for Python2.
Python versions 3.5 through 3.9-beta1 are tested and supported, as well as pypy3.

- Tests moved from unittest to pytest (163)
- Domain and caching support from Flask-BabelEx (163)
- Documentation moved from python-hosted to Github Pages.
- CI moved from Travisci to Github Actions
- Small documentation improvements.
- Removed uncessary checks on get_translations() (127, 126)
- localeselector and timezoneselector can be changed after creation.

Links

• PyPI: https://pypi.org/project/flask-babel
• Changelog: https://pyup.io/changelogs/flask-babel/
• Docs: https://pythonhosted.org/flask-babel/

[pyup-bot]

Closing this in favor of #198