Convert Bite event field types to numeric

- Enables arithmetic operations when constructing views
- Also removes application-level references to DB ID

db/migrations/1534295713_create_bite_table.up.sql

@@ -1,13 +1,13 @@
 CREATE TABLE maker.bite (
   id        SERIAL PRIMARY KEY,
   header_id INTEGER NOT NULL REFERENCES headers (id) ON DELETE CASCADE,
-  ilk       bytea,
-  lad       bytea,
-  ink       VARCHAR,
-  art       VARCHAR,
-  iArt      VARCHAR,
+  ilk       TEXT,
+  urn       TEXT,
+  ink       NUMERIC,
+  art       NUMERIC,
+  iArt      NUMERIC,
   tab       NUMERIC,
-  flip      VARCHAR,
+  nflip     NUMERIC,
   tx_idx    INTEGER NOT NUll,
   raw_log   JSONB,
   UNIQUE (header_id, tx_idx)

db/migrations/1537970059_rename_bite_lad_to_urn.down.sql

@@ -1 +0,0 @@
-ALTER TABLE maker.bite RENAME COLUMN urn TO lad;

db/migrations/1537970059_rename_bite_lad_to_urn.up.sql

@@ -1 +0,0 @@
-ALTER TABLE maker.bite RENAME COLUMN lad TO urn;