Add ESLint support and configure it to use Drupal standards

[hkirsman]

I've started to work on adding javascript linter that uses rules from Drupal here wunderio/code-quality#84

I think we don't have any verification for javascript files out of the box so we should start now. Better late than never.

Drupal project is good case to test and have a discussion.

So an example let's say we have this js file:
var foo="bar"

With ESLint and Drupal rules from web/core/.eslintrc.passing.json, this would be alerted and prompted to be fixed (automatically) to this:
const foo = 'bar'

This is just one small example.

[hkirsman]

I've created PR and waiting for reviews @tormi Who could I invite?