Browser a11y

This is a set of changes to make the browser more accessible.

The tabs are marked up with proper ARIA roles and states, so that the user always knows which the selected tab is.

The lists in the awesomeScreen received the correct ARIA markup so they properly talk.

Modal dialogs have the proper mark up to be read properly by AccessFu.

The URLButton received its alternative text.

The tabs badge at the top right received its proper role.

The context menu is marked up as such.

Unfortunately, I was not able to get GAIA to build in a way that I could test these changes. I tested the individual approaches with small local snippets that mimic the markup used, and those worked fine.