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
Create scroll-to-element module

* Move inline javascript to re-usable javascript module
Update jenkins script to run default rake task

* We need to run JavaScript tests as well now, which have been added to
the default task
Merge pull request #110 from alphagov/jasmine

Add Jasmine for Javascript testing