Introducing Site Icon, favicon management for WordPress.

This v1 marries Jetpack's Site Icon module with the Media Modal, reusing code
from the Custom Header admin. For now, the core-provided icons will be limited
to a favicon, an iOS app icon, and a Windows tile icon, leaving `.ico` support
and additional icons to plugins to add.

Props obenland, tyxla, flixos90, jancbeck, markjaquith, scruffian.
See #16434.



git-svn-id: https://develop.svn.wordpress.org/trunk@32994 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/formatting.php

@@ -3421,6 +3421,7 @@ function sanitize_option( $option, $value ) {
 		case 'thread_comments_depth':
 		case 'users_can_register':
 		case 'start_of_week':
+		case 'site_icon':
 			$value = absint( $value );
 			break;