add formatters/validation via pre-commit/CI

[ltalirz]

Start autoformatting and validating contents of the database

• formatters for line endings, whitespace and json formatting (DB already adheres to these)
• black formatter for python code
• validate uniqueness of DOIs
• check mapping between DOIs and folder names
• check for negative pressures

[ltalirz]

@dwsideriusNIST besides the formatters, I've started adding first validators in .github/validate.py. I think it will be quite easy for you to extend those with additional checks (just modify this file and the .pre-commit-config.yaml).

Note: The check for negative pressures turns up around ~100 isotherms with negative pressures: https://github.com/lsmo-epfl/isodb-library/runs/814328603#step:5:16

Perhaps these should be post-processed via your scripts once more?