Use Jinja2 templates for formatting automatic pages

We already use [Jinja2](https://jinja.palletsprojects.com/en/2.11.x/) in `ExtlinkReplacements`. It would be nice to refactor the `AutoPage` class to support formatting Jinja2 templates. It would be used for these scripts:

- [ ] `list-problematic-pages.py`
- [ ] `sort-maintainers.py`
- [ ] `statistics.py`
- [ ] `toc.py`
- [ ] `update-package-templates.py`