Add raw log to Frob record in DB

- Enables parsing additional values off the log if necessary
- Also update Frob to reflect DSS changes (lad => urn)
- Move Frob constants to shared directory

db/migrations/1533844125_create_frob_table.up.sql

@@ -1,13 +1,14 @@
 CREATE TABLE maker.frob (
   id        SERIAL PRIMARY KEY,
   header_id INTEGER NOT NULL REFERENCES headers (id) ON DELETE CASCADE,
-  tx_idx    INTEGER,
   ilk       bytea,
-  lad       bytea,
+  urn       bytea,
   dink      NUMERIC,
   dart      NUMERIC,
   ink       NUMERIC,
   art       NUMERIC,
-  iart       NUMERIC,
+  iart      NUMERIC,
+  tx_idx    INTEGER NOT NUll,
+  raw_log   JSONB,
   UNIQUE (header_id, tx_idx)
 );