Add ARIA landmarks for Seven theme

Problem/Motivation

As a screenreader user, I need helpful ARIA landmarks so I can efficiently use the Drupal administration screens and jump to the correct parts of each page. The Seven theme for administration tasks needs ARIA landmarks to improve its accessibility.

Proposed resolution

Screenshots are attached showing the proposed ARIA landmarks to apply to different sections of the page on Drupal administration screens in the Seven theme.

The first screenshot shows the basic landmarks that should appear on every page. The second one shows internal landmarks on some pages that have multiple areas of tools. The third screenshot shows that the tabs (primary tabs and secondary tabs) should get a navigation landmark.

Remaining tasks

Based on the screenshots attached, the appropriate ARIA attributes should be added to the specified elements of the admin pages. This should be a simple job of adding appropriate markup into Seven theme template files.

User interface changes

None, except for screenreader users who will be able to navigate within a page using landmarks.

API changes

None.

(Thanks to David MacDonald who works with the W3C and attended the Montreal Drupal Accessibility Sprint for recommendations on these landmarks.)