Custom Page Column: Page Template (Sortable)

add_filter( 'manage_edit-page_columns',          'page_column_views' );
add_filter( 'manage_edit-page_sortable_columns', 'page_column_views' );
function page_column_views( $columns ) {

    $columns['page-layout'] = 'Template';
    return $columns;

}

add_action( 'manage_pages_custom_column', 'page_custom_column_views', 5, 2 );
function page_custom_column_views( $column_name, $page_id ) {

    if ( $column_name === 'page-layout' ) {

        $set_template = get_post_meta( $page_id, '_wp_page_template', true );

        if ( $set_template == 'default' ) {

            echo 'Default';

        }
        else {

            $templates = get_page_templates();
            ksort( $templates );
            foreach ( array_keys( $templates ) as $template ) :
                if ( $set_template == $templates[$template] ) echo $template;
            endforeach;

            echo '<br /><small>' . $set_template . '</small>';

        }
    }

}

add_action( 'pre_get_posts', 'sort_pages_by_page_template' );
function sort_pages_by_page_template( $query ) {

    if ( ! is_admin() )
        return;

    $orderby = $query->get( 'orderby');

    if( 'page-layout' == $orderby ) {
        $query->set( 'meta_key', '_wp_page_template' );
        $query->set( 'orderby', 'meta_value' );
    }

}