Block Reward emission by time

[rstormsf]

Title

  Title: Reward validators by time passed
  Layer: Consensus

Abstract

In order to make a chain consensus agnostic, there is way to reward them by the time passed, not by how many blocks they have validated. Therefore, whenever each block is created, it should save the timestamp and check the diff between last time the block was validated. If there is minimum threshold archieved (5 sec, for example) it should reward next validator from the array list to issue 1 reward (POA).
Smart contract should handle the state the order of last rewarded validator.

Rationale

In order to try different consensus algorithms, such as honeybadger BTF, we have to come up with different way to archive validator's incentive.

[varasev]

The BlockReward smart contract has been complemented by the logic described above. It's been done in poanetwork/poa-network-consensus-contracts#133.

[varasev]

Reward by time logic has been moved to separate RewardByTime contract: poanetwork/poa-network-consensus-contracts#140