Add Grunt-powered Jasmine spec runner and a first spec

Hi Chosen,

as mentioned in #1401 there seems to be some appetite for introducing testing to chosen.

This pull request does exactly that by using the great jasmine spec runner for Grunt. It installs phantomjs through npm and uses that to run the tests. If you're not familiar with phantomjs: it's a headless webkit browser that is as good as a real browser.

The specs themselves are fairly simple so far but I tried to show an example of constructing a chosen element entirely in memory, doing some interactions on it and asserting the expected result.

If you want to run the test just do a
```
npm install
grunt test
```

If you have any questions, please shoot. I'd love to incorporate your feedback into this PR.