Store reference to included block in transaction

[shuse2]

Description

Add BlockID property when storing the block, and it should return in the response from the RPC.
There should be distinction between general Transaction concept which used inside of block or in transaction pool. Therefore, Transaction struct should remain as it is.

Motivation

Currently, there is no information about in which block the transaction is included when transaction is fetched from storage.
This will make other system hard to link the block when fetching single transaction