added a phantomjs browser with spec

Notes from the ticket:

> Added phantom support with an additional browser, appears to have some native support in the ruby Gem as detailed here: https://github.com/SeleniumHQ/selenium/pull/8

> Could use some refactoring... perhaps the runner itself can return an appropriately configured driver, as the init_driver method has to switch between things... will open a pull request.

After running through some scenarios, headless support was a little easier than expected. Some suggestions I had:

- add a simple rake build system to automate the testing
- package a static version of the se-server jar with the code base or declare an explicit dependency on a specific version to streamline the testing


My understanding now is that basically the main `SeleniumConnect` class is saying:

> Given a configuration, I should provide a driver class.

If that is the case then we might be able to more cleanly encapsulate the driver construction in the individual runner classes themselves. 

Anyway let me know if this works for headlessness :P