Setup testing for gem using dummy application

* Test JavaScript using Jasmine
* Test template includes with Capybara/RSpec
  * Symlink dummy specs with spec directory for smoother RSpec testing
* Make `bundle exec rake` default to running all tests
* Make the dummy app (spec/dummy) resemble an app that's using the gem
  * Include govuk_admin_template js and css, and incorporate template
* Include jQuery dependency — Bootstrap depends on jQuery being present within the template

__Dummy application when running:__

![screen shot 2014-05-16 at 15 40 56](https://cloud.githubusercontent.com/assets/319055/2998226/20971c84-dd08-11e3-8e46-78f9baf59776.png)