Add demo invocation of frost-link with tabindex
Add demo invocation of frost-link with tabindex

`frost-link` inherits from Ember.LinkComponent, and already supports
tabindex.  It will render as an `<a>` component already, so there is no
need for us to pass anything to a deeper child component.

sglanzer/ember-frost-core,ciena-frost/ember-frost-core,EWhite613/ember-frost-core,dafortin/ember-frost-core,helrac/ember-frost-core,sglanzer/ember-frost-core,vesper2000/ember-frost-core,vesper2000/ember-frost-core,helrac/ember-frost-core,vesper2000/ember-frost-core,dafortin/ember-frost-core,rox163/ember-frost-core,rox163/ember-frost-core,ciena-frost/ember-frost-core,rox163/ember-frost-core,dafortin/ember-frost-core,sglanzer/ember-frost-core,EWhite613/ember-frost-core,ciena-frost/ember-frost-core,helrac/ember-frost-core,EWhite613/ember-frost-core