fix(demo): Scroll to element on initialization
feat(rating): make widget accessible

 * Support keyboard navigation.
 * Add WAI-ARIA markup.
 * Text representation for screen readers.

Source: http://mindtrove.info/creating-an-accessible-internationalized-dojo-rating-widget/

Closes #1707
refactor(tabs): use optional binding for `active`

Closes #1713
fix(tabs): remove `tabbable` class required for left/right tabs

Closes #1708