Implement compression quota refunds and admin manual subscription

migrations/004_add_bonus_units.sql

@@ -0,0 +1,11 @@
+BEGIN;
+
+ALTER TABLE usage_periods
+  ADD COLUMN IF NOT EXISTS bonus_units INTEGER NOT NULL DEFAULT 0;
+
+UPDATE usage_periods
+SET bonus_units = bonus_units + ABS(used_units),
+    used_units = 0
+WHERE used_units < 0;
+
+COMMIT;