[WIP] Functional testing

@harvesthq/chosen-developers: What do you guys think of functional testing?

I'm not that familiar with testing, but tried to set up the basics using capybara and poltergeist.

Some to-do points:

- [ ] **Single tests**

    - [ ] Single with selected
    - [ ] Single with disabled
    - [ ] Single with deselect
- [ ] **Multi tests**

  - [ ] Multi with selected
  - [ ] Multi with disabled
  - [ ] Multi with max

- [ ] **Use separate test html files instead of example pages**


To be able to run the tests the following steps must be completed:
- install the required gems by running `bundle install`
- download and install [phantomjs](http://phantomjs.org/download.html)

To run the tests simply execute `rspec`