Tab Component lacks accessible role="tab"

The [ember-paper Tabs](https://miguelcobain.github.io/ember-paper/#/components/tabs) component renders a wrapper element with a `role='tablist`, which is a superb start. However, an element with this role _requires_ a child element to have a `role='tab'` https://dequeuniversity.com/rules/axe/3.5/aria-required-children?application=axeAPI.

Running a `a11yAudit` with popular [`ember-a11y-testing` addon](https://github.com/ember-a11y/ember-a11y-testing) fails with a `aria-required-children` rule violation.