chore: add eslint/prettier and npm task

[escapedcat]

Background for this PR

Linting the code will make sure on the long run code is consistent. Every touched or newly added code will be linted.
Prettier takes care of formatting the code. Eslint will take care of checking the JS-parts and providing info on what should be improved.

You can always skip linting using --no-verify during a commit.

To let prettier do it's job on "file save" in code you can install this extension: https://marketplace.visualstudio.com/items?itemName=esbenp.prettier-vscode

[clayrab]

This would be nice...

[escapedcat]

After this is merged we should add a check to Github-actions for this as well