Vat.fold: store ilk and urn as text instead of bytea

db/migrations/1538510582_create_vat_fold_table.up.sql

@@ -1,8 +1,8 @@
 CREATE TABLE maker.vat_fold (
   id            SERIAL PRIMARY KEY,
   header_id     INTEGER NOT NULL REFERENCES headers (id) ON DELETE CASCADE,
-  ilk bytea,
-  urn bytea,
+  ilk text,
+  urn text,
   rate numeric,
   tx_idx        INTEGER NOT NULL,
   raw_log       JSONB,

db/schema.sql

@@ -704,8 +704,8 @@ ALTER SEQUENCE maker.tend_id_seq OWNED BY maker.tend.id;
 CREATE TABLE maker.vat_fold (
     id integer NOT NULL,
     header_id integer NOT NULL,
-    ilk bytea,
-    urn bytea,
+    ilk text,
+    urn text,
     rate numeric,
     tx_idx integer NOT NULL,
     raw_log jsonb