Update schemas and resolve some warnings

migrations/20210623000000_reminder_message_embed.sql

@@ -46,7 +46,7 @@ CREATE TABLE reminders_new (
     PRIMARY KEY (id),
 
     FOREIGN KEY (`channel_id`) REFERENCES channels (`id`) ON DELETE CASCADE,
-    FOREIGN KEY (`set_by`) REFERENCES users (`id`) ON DELETE SET NULL
+    CONSTRAINT `reminders_ibfk_2` FOREIGN KEY (`set_by`) REFERENCES `users` (`id`) ON DELETE SET NULL
 
     # disallow having a reminder as restartable if it has no interval
     -- , CONSTRAINT restartable_interval_mutex CHECK (`restartable` = 0 OR `interval` IS NULL)