- removed a few enabled rules which we are already using the default values
- enabled a few for strictness
@Johann-S: I know we disagreed last time on undefined but I still believe we should enable this. That being said, the other changes are good too, so I can revert that part if you insist.
We should also discuss which other rules we might enable. I know for sure I'd like semicolons, but it's a personal matter of taste plus this would conflict with your other PRs so it's something we should do in the future, if ever.