Create accessibility demo page for Tabs

[tinayuangao]

Bug, feature request, or proposal:

What is the expected behavior?

What is the current behavior?

What are the steps to reproduce?

Providing a Plunker (or similar) is the best way to get the team to see your issue.
Plunker template: https://goo.gl/DlHd6U

What is the use-case or motivation for changing an existing behavior?

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

Is there anything else we should know?

[angular-automatic-lock-bot]

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