housekeeping: explore using poetry for dependency management and scripts

[JanKoppe]

Let's take a look at using https://python-poetry.org/ to manage the project a bit more. Right now there's just a requirements.txt that is managed by hand and nothing else. I think having a well-managed poetry configuration to declare and manage dependencies would be a great start.

additionally it could be possible to combine common commands (test-suite, building frontend-assets, collecting static files, seeding database, etc) in this config, to make working with the project a bit easier!