paper-dialog: escape key does not always close dialog with escapeToClose=true

Because the keydown event is scoped to the component, the escape key is not always closing the dialog modal.

I don't know if it works as intended but if you take the [demo](http://miguelcobain.github.io/ember-paper/release-1/#/components/dialog), click on "custom dialog" then anywhere within the dialog, the escape key won't close the dialog anymore.