Issue 11/selenium instance

Hi,
I added regular selenium standalone selenium support, through a 'selenium' option.

```
selenium: {
    hostname: '127.0.0.1',
    port: 4444
}
```

I had to split the grunt test task in 2, because I am not sure how/if it is possible to start selenium on travis.

So travis tests are still started using ``grunt test`` (which does not include selenium tests), and I added ``grunt testSelenium``.

Also, some refactoring can probably be done to reuse browsers to the queue, let me know if you want me to refactor this part a little bit (or feel free to do it!)à