[SC] Optimization of the frequent RPC requests

[hyunsooda]

The current RPC handler implementation in SC has unnecessarily frequent transfer logic. For example,

Sender                                 Receiver 
Send _txreq_         -------------->  
Send _receiptreq_ --------------> 
Send again if the receipt didn't arrived:
  Send _txreq_         -------------->  
  Send _receiptreq_ -------------->

                    <--------------   Send _receiptres_

The sender sends two requests. If the receiver runs a thread that sends a receipt response when a receipt is in a new block, It can be reduced to one request. However, it accompanies somewhat a little change in the implemented RPC structure.

[hyunsooda]

The bridge tx receipt is created on the counterpart chain and thus the receipt request is required unless the mainbridge node pushes to subbridge node a corresponding receipt of the bridge tx. However, the request-response handler pair can be changed to a single request message manner. (e.g., pull manner to push manner), but it requires an addition to the chain head event on the mainbridge node that tracks the corresponding tx receipts.

[exalate-issue-sync]

Exalate commented: Issue Created by: hyunsooda