Bug 1068698 - Email list should be listbox with list items.

This takes this line a bit over 80 characters, and we want to get the HTML files within the max 80 character lines used for the JS files. We usually break the HTML tag at an attribute name and indent it to align with the attribute in the line above:

```html
 <div data-prop="messagesContainer" class="msg-messages-container"
      role="listbox">
```

With that change and a rebase to just one commit in the pull request, this should be easy to land.