Install jQuery, QUnit, Sinon, and Sinon-QUnit, then add a basic example test

The Sinon package in Bower is broken, so we use the static version instead.
Add tests for default keyboard navigation behavior

We can't directly test redirection via window.location, so I've created a
TwentyFourteen namespace and moved the actual navigation call into a new
`TwentyFourteen.navigate` method. This allows us to stub out the navigation
itself within the tests, to verify that everything else works as expected.