Improving Eslint rules

[khenriksson]

Currently it's rather annoying when developing and everything turns red because eslint isn't completely configured correctly, as we can see from the terminal as well during development. I would suggest going through the eslint config and check out the way we want to configure the project, and maybe also add prettier on the side.

[pholm]

I noticed the same while uprading linting related libraries. (#453) Especially in the new version where build fails if there is lint errors, this would be quite essential.