Reformat repo using eslint rools

[ChromeGG]

Currently, eslint is throwing a lot of obvious errors like:

They're easy to fix (most of them are auto-fixable). But the diff will be huuuuge. That's why I want it in a separate issue.

So on this ticket, I'll:

1. Add sonarJS plugin for eslint.
2. Fix all eslint errors.
3. (Optionally) Provide a GH action that runs eslint before merging to master.

@dohomi Let me know what you think about that. If you wanna provide some other eslint rules, feel free 😃

[dohomi]

@ChromeGG feel free to open a PR with different eslint settings.