add support to test in browsers via zuul

Adds support to test the module in browsers via [zuul](https://github.com/defunctzombie/zuul). Out of the box you can just do

```shell
npm run test-local
```

And it will give you a URL you can open in a local browser to see the tests run. The project has also been setup to test in cloud browsers. You will need a free saucelabs account to do this. I have documented everything you need to get started on the [zuul wiki](https://github.com/defunctzombie/zuul/wiki). Happy to answer any questions here or on stackvm :)