Input submit CSS classes overrides

With this patch we can alter now the predefined array of the classes:

Example:

function my_belgrade_subtheme_belgrade_submit_button_class_alter(&$text_data) {
  $text_data['matches'][t('Add to cart')->render()] = 'add-to-cart';
}

Works great. Thanks @khiminrm.

Automatically closed - issue fixed for 2 weeks with no activity.