Either fix or except all eslint offences
In this small MR we start enforcing all eslint rules. This will make it easier for anyone to contribute.
This change would be best reviewed by commits. First, we introduce the
autofix npm task and let if fix all eslint issues that can be automatically fixed.
In the following commits, all the other eslint offences get either fixed or prepended with
// eslint-disable-next-line exception.
Closes #217 (closed)