Add feature handlebar/DOM element test with jest

[martinchuka]

What?

This will add the ability to directly add test for DOM elements including the handlebar generated elements using jest/jsdom

Sample test for templates/pages/home.html is available within assets/js/test-unit/theme/pages/home.spec.js

Tickets / Documentation

• N/A

Screenshots (if appropriate)

• N/A

Thanks, @carsonreinke for helping me out with the code review :thumbsup:

[bigbot]

Autotagging @bigcommerce/storefront-team @davidchin