(Fix) 2_deploy_contract.js for correct deployment of RewardByBlock

[varasev]

• (Mandatory) Description The migrations/2_deploy_contract.js script deploys RewardByBlock contract without changing the constant emissionFunds that stores an address of EmissionFunds contract: https://github.com/poanetwork/poa-network-consensus-contracts/blob/a8820e1f0040fb567ba55b390d3b54fcd55b6f65/contracts/RewardByBlock.sol#L21 - this behavior is incorrect, so this PR repairs it. Should be merged after https://github.com/poanetwork/poa-network-consensus-contracts/pull/197 is merged.

• (Mandatory) What is it: (Fix), (Feature), or (Refactor) (Fix)

[varasev]

All refactoring suggestions were implemented in https://github.com/poanetwork/poa-network-consensus-contracts/pull/198/commits/fdfe738eeca2569325cd54dd3e96035e489149f7 except installing of web3 package - I think we don't need it because truffle already contains web3 0.20.x which solves the task almost the same way.