Proper heading for admin screens.

First step towards restoring a good heading structure in wp-admin.
The previous `<h1>` contained the site title and a link to the front page and was removed with the toolbar refactoring in 3.2.

Props joedolson, afercia.
Fixes #31650.


Built from https://develop.svn.wordpress.org/trunk@32974


git-svn-id: http://core.svn.wordpress.org/trunk@32945 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/network/upgrade.php

@@ -39,7 +39,7 @@ if ( ! current_user_can( 'manage_network' ) )
 	wp_die( __( 'You do not have permission to access this page.' ), 403 );
 
 echo '<div class="wrap">';
-echo '<h2>' . __( 'Upgrade Network' ) . '</h2>';
+echo '<h1>' . __( 'Upgrade Network' ) . '</h1>';
 
 $action = isset($_GET['action']) ? $_GET['action'] : 'show';