ES7 Migration - Linting

[oshalygin]

In an effort to keep the codebase manageable with numerous contributors, it would be helpful if we had a linter in place. The obvious choice is ESLint, followed by the specific style guide that we can start with and then customize accordingly.

I'll make some propositions:

• Airbnb styleguide: https://github.com/airbnb/javascript
• Prettier alongside the airbnb guide: https://github.com/prettier/prettier

[cybertk]

+1 for Airbnb