Update no-empty-attrs rule

[clcuevas]

I am introducing this change to the no-empty-attrs rule because I have found that it makes more sense to send ESLint report errors on a per-attr property basis. This way, we can use ESLint's inline comments to disable this rule for specific attr properties rather than the entire Model.

[michalsnik]

Thanks @clcuevas! This makes total sense. However could you please add some test examples regarding this change?

It's possible to check whether given error occurred on specific line:

errors: [{
  message: 'Something bad happened',
  line: 4,
}]

That would makes this PR complete and I'll be happy to merge this :)

[clcuevas]

@michalsnik Thanks for the heads up on the tests! Should be good to go for another review.

[michalsnik]

Thanks @clcuevas! Looks great :)