stats: limit results to fit into discord message limit

PresenceTracker.py

@@ -98,7 +98,8 @@ class PresenceTracker:
             'left join activities a on a.id = presence_journal.activity_name_id '
             'where user_id = ? '
             'group by activity_name_id '
-            'order by total desc;',
+            'order by total desc '
+            'limit 20;',
             (user_id,)
         ).fetchall()