Keyboard accessibility for the media modal:

* Arrow keys navigate between items in the grid.
* Transfer focus into the panel when selecting a tab along the side.
* Transfer focus into the details sidebar when selecting an item and vice versa.
* Set initial focus on the close button so that it is visible.

props celloexpressions, lessbloat, ericlewis. fixes #25100, #25101, #28704. see #23560.

Built from https://develop.svn.wordpress.org/trunk@29220


git-svn-id: http://core.svn.wordpress.org/trunk@29004 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Tie cookies and nonces to user sessions so they may be invalidated upon logout.

Sessions are stored in usermeta via WP_User_Meta_Session_Tokens, which extends the abstract WP_Session_Tokens class. Extending WP_Session_Tokens can allow for alternative storage, such as a separate table or Redis.

Introduces some simple APIs for session listing and destruction, such as wp_get_active_sessions() and wp_destroy_all_sessions().

This invalidates all existing authentication cookies, as a new segment (the session token) has been added to them.

props duck_, nacin, mdawaffe.
see #20276.

Built from https://develop.svn.wordpress.org/trunk@29221


git-svn-id: http://core.svn.wordpress.org/trunk@29005 1a063a9b-81f0-0310-95a4-ce76da25c4cd