[Wordpress] Set the MENU ORDER as the default sorting order for PAGES in ADMIN. Source: http://wordpress.org/support/topic/sort-pages-by-date-in-admin-by-default?replies=4#post-5380257

wp-admin-pages-orderby-menuorder.php

<?php

/**
 * Order Admin Pages by Menu Order by Default
 *
 * Source:
 * http://wordpress.org/support/topic/sort-pages-by-date-in-admin-by-default?replies=4#post-5380257
 *
 */
add_filter('pre_get_posts', 'my_set_post_order_in_admin' );
function my_set_post_order_in_admin( $wp_query ) {
	global $pagenow;
	if ( is_admin() && $_GET['post_type'] == 'page' && 'edit.php' == $pagenow && !isset($_GET['orderby'])) {
		$wp_query->set( 'orderby', 'menu_order' );
		$wp_query->set( 'order', 'ASC' );
	}
}