Tabs should follow WAI-ARIA guidelines

Problem/Motivation

So that people with disabilities can use the widget easily, it's best that the widget markup and functionality conform to the guidelines laid out by the ARIA Authoring Practices guidelines for tabs.

For example, we could expect to see:

• ARIA roles on the tabs and their corresponding tab panels;
• ARIA attributes as appropriate, such as aria-selected
• keyboard operability, including supporting the arrow keys

Proposed resolution

We should update the JavaScript library to add these accessible semantics and support keyboard functionality.

API changes

While changing the actual tag themselves would be desirable, it may be possible to implement these changes solely through adding HTML attributes.

Data model changes

I don't believe there would be Data model changes