Add Pit file debt ceiling event

db/migrations/1535667935_create_pit_file_table.down.sql

@@ -1,2 +1,3 @@
 DROP TABLE maker.pit_file_ilk;
-DROP TABLE maker.pit_file_stability_fee;
+DROP TABLE maker.pit_file_stability_fee;
+DROP TABLE maker.pit_file_debt_ceiling;

db/migrations/1535667935_create_pit_file_table.up.sql

@@ -17,4 +17,14 @@ CREATE TABLE maker.pit_file_stability_fee (
   tx_idx    INTEGER NOT NULL,
   raw_log   JSONB,
   UNIQUE (header_id, tx_idx)
-)
+);
+
+CREATE TABLE maker.pit_file_debt_ceiling (
+  id SERIAL PRIMARY KEY,
+  header_id INTEGER NOT NULL REFERENCES headers (id) ON DELETE CASCADE,
+  what      TEXT,
+  data      NUMERIC,
+  tx_idx    INTEGER NOT NULL,
+  raw_log   JSONB,
+  UNIQUE (header_id, tx_idx)
+);