Add jasmine via official jasmine gem

* Run `rails g jasmine:install`
* Configure to avoid default phantomjs download
Include jasmine:ci in default task

* Run javascript tests by default
Include govuk-admin-template as jasmine src file

* Required for bootstrap and jquery libraries to be present
Create rudimentary chosen module

* Start chosen select drop downs based on data attributes rather than
CSS classes
Merge pull request #244 from alphagov/jasmine

Add Jasmine for Javascript testing