Introduce constant TB_OBJECT_MODELS_AUTHORITATIVE

This constants exists to tell CoreUpdate to consider object models definitions
as an ultimate source of truth. Database tables will be migrated to match
these definitions if there any differences in table structure are found.

Because this constant didn't exist in older version of thirtybess, using core updater
to downgrade to older version will not trigger any database migration

config/config.inc.php

@@ -39,6 +39,16 @@
 
 $start_time = microtime(true);
 
+/**
+ * This constants exists to tell CoreUpdate to consider object models definitions
+ * as an ultimate source of truth. Database tables will be migrated to match
+ * these definitions if there are any differences.
+ *
+ * Because this constant didn't exist in older version of thirtybess, downgrading will
+ * not trigger any database changes
+ */
+define('TB_OBJECT_MODELS_AUTHORITATIVE', true);
+
 /* SSL configuration */
 define('_PS_SSL_PORT_', 443);