WP NEXT/PREV

/* Add Next Page Button in First Row */
add_filter( 'mce_buttons', 'my_add_next_page_button', 1, 2 ); // 1st row

/**
 * Add Next Page/Page Break Button
 * in WordPress Visual Editor
 *
 * @link https://almasira.org/2046
 */
function my_add_next_page_button( $buttons, $id ){

    /* only add this for content editor */
    if ( 'content' != $id )
        return $buttons;

    /* add next page after more tag button */
    array_splice( $buttons, 13, 0, 'wp_page' );

    return $buttons;
}
/* Add Next Page Button in First Row */