Increase block cache size to 400k for faster wallet sync

- Increase default cache-size from 40,000 to 400,000 blocks
- Add Python gRPC protobuf bindings for testing

common/common.go

@@ -258,6 +258,12 @@ func GetBlockRange(rpcClient *rpcclient.Client, cache *BlockCache,
 			return
 		}
 
+		if block == nil {
+			errOut <- errors.New(
+				fmt.Sprintf("Block %d was nil without error", i))
+			return
+		}
+
 		blockOut <- *block
 	}