Add multi-variant test sets

administrator/components/com_testquestions/sql/install.mysql.utf8mb4.sql

@@ -40,6 +40,8 @@ VALUES (1, 'Bez kategorii', 1, 0);
 
 CREATE TABLE IF NOT EXISTS `#__testquestions_sets` (
   `id` int unsigned NOT NULL AUTO_INCREMENT,
+  `parent_id` int unsigned NOT NULL DEFAULT 0,
+  `set_type` varchar(12) NOT NULL DEFAULT 'ordinary',
   `subject_id` int unsigned NOT NULL DEFAULT 0,
   `title` varchar(255) NOT NULL,
   `duration` smallint unsigned NOT NULL DEFAULT 0,
@@ -54,6 +56,7 @@ CREATE TABLE IF NOT EXISTS `#__testquestions_sets` (
   `modified_by` int unsigned NOT NULL DEFAULT 0,
   PRIMARY KEY (`id`),
   KEY `idx_published` (`published`),
+  KEY `idx_parent_id` (`parent_id`),
   KEY `idx_ordering` (`ordering`)
 ) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 DEFAULT COLLATE=utf8mb4_unicode_ci;