Customizer: Use deep-links for Backgrounds, Headers, and Widgets.

Replace links in admin menu and toolbar to Custom Background/Header screen with deep-links to the Customizer section.
On the Widgets screen display a link to the Customizer widgets panel.

props topher1kenobe, rzen, celloexpressions, westonruter
fixes #25569, #25571, #28032.
Built from https://develop.svn.wordpress.org/trunk@30459


git-svn-id: http://core.svn.wordpress.org/trunk@30450 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/css/admin-menu-rtl.css

@@ -610,6 +610,11 @@ li#wp-admin-bar-menu-toggle {
 	display: none;
 }
 
+/* Hide-if-customize for items we can't add classes to */
+.customize-support #menu-appearance a[href="themes.php?page=custom-header"],
+.customize-support #menu-appearance a[href="themes.php?page=custom-background"] {
+	display: none;
+}
 
 /* Auto-folding of the admin menu */
 @media only screen and (max-width: 960px) {

wp-admin/css/admin-menu.css

@@ -610,6 +610,11 @@ li#wp-admin-bar-menu-toggle {
 	display: none;
 }
 
+/* Hide-if-customize for items we can't add classes to */
+.customize-support #menu-appearance a[href="themes.php?page=custom-header"],
+.customize-support #menu-appearance a[href="themes.php?page=custom-background"] {
+	display: none;
+}
 
 /* Auto-folding of the admin menu */
 @media only screen and (max-width: 960px) {