Make repo more usable for others

[niklasbogensperger]

• add docstrings to functions and provide some documentation (i.e. expand README and db_setup.ipynb) instead of spurious comments
• make the whole codebase a bit less hardcoded
• purge files with access tokens or personally identifiable information from the repo and its history

[hoengggroup]

Tokens, credentials, IDs, etc. and some no longer needed large binary files (pickle files, databases) were purged using https://rtyley.github.io/bfg-repo-cleaner/ on 2022-05-18.
The only pull request used for the initial development of the postgresql database had to be deleted by GitHub Support in order to purge unupdatable references to the old commit tree.

[hoengggroup]

Some more old pickle save files and selenium binaries were purged on 2022-05-19.