PhantomJSDriver support added.


Added PhantomJS support through [GhostDriver](https://github.com/detro/ghostdriver) and its PhantomJSDriver  Java bindings. 

To use this driver, you need to:

- Download PhantomJS from http://phantomjs.org/download.html
- Add the following to your runner class:

        System.setProperty(PhantomJSDriverService.PHANTOMJS_EXECUTABLE_PATH_PROPERTY,
        "location/phantomjs-x-y/bin/phantomjs");

- Because PhantoJS is really fast, make sure to increase the waiting times in Crawljax configuration.