Add validation logic for blocks and transaction root

[ishantiw]

Description

Add static validation logic for incoming blocks as described in LIP0063

This function is called from sync function and it can be a util function like below,

validateBlock(receivedBlock: Buffer, deserializedNextBlock)

Validation:

• To calculate blockID of the incoming block and check its blockID with previousBlockID of the block at height h + 1
  • Calculate the block ID from the received blockBytes and compare with previousBlockID
• Should pass schema check as given for that range of blocks
• Deserialize the block
• Payload should be checked against transactionRoot by calculating transactionRoot from the payload using MerkleTree

Acceptance Criteria

• Should have unit tests covering the validation steps