problem: some JSON RPC client cannot use IDs and process response by their order

solution: add option to preserve batch request-response correspondence order
rel: #148

src/test/resources/dshackle-proxy-max.yaml

@@ -2,6 +2,7 @@ proxy:
   enabled: true
   host: 0.0.0.0
   port: 8080
+  preserve-batch-order: true
   routes:
     - id: ethereum
       blockchain: ethereum