AppNavigation is still traversable when closed

[danxuliu]

When the AppNavigation is closed it is moved outside of the viewport. However, its contents are still in the DOM and, technically, visible, so they are still focusable and pressing tab traverses them.

Note that the AppNavigation as a whole can not be hidden when closed, as the toggle to show it again is also part of it; only the list and the footer should be hidden.

Steps to reproduce

• Open Talk or Mail
• Close the app navigation
• Traverse the UI pressing tab

Expected result

The button to toggle the navigation bar is traversed, but nothing else from the AppNavigation is

Actual result

The contents of the navigation bar are traversed