Initial refactoring for standardizing linting and testing

[cmin764]

Dependency of #14

Adds a thin layer of not too opinionated formatting (from our configuration intervention/deviation PoV):

• Linting: isort, black, flake8/pep8 (exception for the line length 88 -> 120 chars; TBD)
• Beta 1.0.0 release with package updates included
• Applies current rules into formatting through inv lint -a command

❗ By any means this doesn't and shouldn't change behaviour, it's only a cosmetic refactoring aided by Invoke through Poetry commands.

ToDo

• Refactor the entire test with pytest. (and fixtures for the JAB wrapper and context tree)
• Add build and publish (CI/prod) Invoke commands.
• Add simple README section with:
  • How to quickly isolate the env preparation with pyenv. (so Poetry and Invoke are made available)
  • How to setup Poetry config and credentials. (for CI/prod package publishing)

Check updated README Development instructions

[mmokko]

Looks good, I'll add the pipeline and merge.