Add jasmine-rails to run JavaScript tests

For use in the JavaScript that is being written for the checkbox drop
downs.

- Add `jasimine-rails` gem to `Gemfile`
- Mount test runner on `/spec` so tests can be run in browser
- Add `jasmine_rails.rake` rake task so that tests are run by default
  when you call `bundle exec rake`
- Add a line to `test.rake` so the tests are run when you call
  `bundle exec rake test`
- Add a dummy test to prove concept, this should be removed when a real
  test is added
- Add copy of jQuery to helpers. This is normally included on pages
  using static/slimmer but won't be available in tests
- Add config for `jasmine-rails`
Add primary link JavaScript

- Add primary link JavaScript to enable hiding links from a list.
- Move jquery isn't a `src_files` block in jasmine config as it needs to
  exist before the application.js
- Add startup block to application.js
Move JavaScript defualt test runner to Rakefile
Merge pull request #4 from alphagov/hide-extra-links

Add primary link JavaScript