VDB-117: Add Vow.flog transformer (#80)

* Add DB migrations for flog

* Add Vow addresses and constants

* Add err logging to ABI signature getter, test for flog sig

* Add flog transformer

* Add tests+data for flog transformer

* Prepend DB tables and columns with vow_

* Panic on failure to get method sig

test_config/test_config.go

@@ -89,6 +89,7 @@ func CleanTestDB(db *postgres.DB) {
 	db.MustExec("DELETE FROM maker.drip_file_repo")
 	db.MustExec("DELETE FROM maker.drip_file_vow")
 	db.MustExec("DELETE FROM maker.flip_kick")
+	db.MustExec("DELETE FROM maker.vow_flog")
 	db.MustExec("DELETE FROM maker.flop_kick")
 	db.MustExec("DELETE FROM maker.frob")
 	db.MustExec("DELETE FROM maker.pit_file_debt_ceiling")