Enforce prettier styling

[hoelger]

For me npm run-script lint-fix and npm run-script postlint-fix don't really run prettier or the styling as expected.

We need:

• The procedure/commands documented in the README and
• Once you set up everything correctly (e.g. with pre-commit) you're acutally forced to comply to the styling rules

[hoelger]

newline after imports

[hoelger]

terminating newlines