Archive old migrations (#426)

* Archive old migrations

* Fix invalid placement of migrations

migrations/archive/000.488.sql

@@ -0,0 +1,4 @@
+ALTER TABLE orders ADD COLUMN purchase_event_sent timestamp with time zone DEFAULT NULL;
+
+-- Populate existing fields so we won't resend purchase events on visits to thank you pages
+UPDATE orders set purchase_event_sent = now();