updated ERC20GatewayBase, ConsensusGateway and ConsensusCogateway.
updated unit tests for ConsensusCogateway::confirmDeposit()
updated unit tests for ERC20GatewayBase::hashWithdrawIntent()
unit tests for ConsensusGateway::confirmWithdraw() are skipped now and will be handled in integration tests
Reason : populating valueToken is necessary in proof file after generating proof. So that it can be used while testing ConsensusGateway::confirmWithdraw(). While testing valueToken is making a transaction hence, it can be handled in integration tests.
Fixes #268