Form: rename 'content_below' to 'buttons_extra'

controllers/EditTag.php

@@ -106,7 +106,7 @@ class EditTag extends HTMLController
 
 		$form = new Form([
 			'request_url' => BASEURL . '/edittag/?' . ($id_tag ? 'id=' . $id_tag : 'add'),
-			'content_below' => $after_form,
+			'buttons_extra' => $after_form,
 			'fields' => $fields,
 		]);