Accommodate GQL optimizations in codegen (#254)

* Prune optional methods in indexer and database interfaces

* Implement GQL optimization changes in codegen

* Fix graph-node test indexer

* Add demos to codegen package

packages/graph-node/test/utils/indexer.ts

@@ -244,4 +244,16 @@ export class Indexer implements IndexerInterface {
   async resetWatcherToBlock (blockNumber: number): Promise<void> {
     return undefined;
   }
+
+  cacheContract (contract: ContractInterface): void {
+    return undefined;
+  }
+
+  async processInitialState (contractAddress: string, blockHash: string): Promise<any> {
+    return undefined;
+  }
+
+  async processStateCheckpoint (contractAddress: string, blockHash: string): Promise<boolean> {
+    return false;
+  }
 }