Full switch to poetry

[carmenbianca]

I was doing some package maintenance for Fedora. This should make my life a whole lot easier.

Maybe postpone this for 2.0 major release.

TODO:

• Translation build step.
• Don't install dev requirements in Docker images and reuse GitHub workflow
• Fix Docker containers
• Fix documentation
• Change log
• Create issue for Python 3.6 deprecation (see if there's inconvenient code in the codebase that exists only for Py3.6 compatibility)
• Write message to reuse mailing list
• Test poetry publishing
  • Signed releases?
• Fix python-debian dependency
  • Ideally, ship with dep5 parser microlibrary.
• Replicate and document make test / make lint.
• Fix pylint pre-commit.