Add web tests

Use testling to run the tests in a browser.

With this configuration the tests are run in a browser automatically when running `grunt test`. The tests will also be executed on Travis CI. In addition to this I can only recommended to integrate these tests with the Testling CI service to get a [badge](https://github.com/bripkens/json-template-generator). Using the Testling CI service is easy. It only takes five minutes. Check out the [testling quick start guide](configuring the web hook) (starting from the *configuring the web hook* section).

You will need the following webhook configuration options for GitHub (to be typed in under this repository's settings):

- payload url: http://git.testling.com
- content-type: form encoded
- secret: <your secret>
- which events?: just the push event
- active: yay

Fixes #3