Update package metadata structure and pipeline

[bvdvecht]

Currently this package relies on some non-standard files and methods for testing, installing and distributing:

• a custom Makefile is used for testing and installing
• dependencies are listed in separate .txt files
• config files are scattered: there are many different files: .flake8, mypy.ini, MANIFEST.in, setup.cfg, pyproject.toml

Also, packaging and distribution to PyPI is not automated.

Ideally, metadata for configuration, installing, testing etc. should all be following some standard format (which one is to be decided), preferably with fewer separate files. This new format should also enable automatic distribution to PyPI, e.g. as a Github Actions workflow.