Add PhantomJS runner

:construction: 

This pull request adds a very basic runner for getting the unit tests to run in PhantomJS. The idea is that we can run this in Travis along with the node tests, and feel safer that the tests will stay green in browser environments also.

You can run it with

```
$ test/phantom/run.sh
```

If anyone could give me a hint on how to elegantly kill off the python process when PhantomJS is done, it'd be greatly appreciated!

##### TODO
- [ ] Stop leaking a python process after each run
- [ ] Fix failing test