Issue 11/selenium instance

Hi,
I added regular selenium standalone selenium support (issue #11 ). If a hostname option is specified, then it runs the tests in selenium mode (if no hostname option, then saucelabs will be used). Added grunt options, based on named parameters for wd.remote() and wd.promiseChainRemote():

```
    hostname: '127.0.0.1',
    port: 4444,
    auth: 'username:pwd'   // optional

```

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``.

## Edit

Apparently, selenium tests can run directly on travis (firefox only) through xvfb (more info [here](http://about.travis-ci.org/docs/user/gui-and-headless-browsers/), but I didn't give it a try (not really familiar with it).