Add ERC20 token watcher example

- starting with the totalSupply function
- sets contract config on transformer by passing it into the transformer
initializer
- handles block records with the same number for different nodes for both creating token_supply records, and finding missing blocks

test_config/test_config.go

@@ -70,3 +70,8 @@ func NewTestDB(node core.Node) *postgres.DB {
 	db.MustExec("DELETE FROM log_filters")
 	return db
 }
+
+func NewTestDBWithoutDeletingRecords(node core.Node) *postgres.DB {
+	db, _ := postgres.NewDB(DBConfig, node)
+	return db
+}