Ethereum Classic Monetary Policy (#5741)

* Ethereum Classic Monetary Policy

Create a new parameter `ecip1017EraRounds`. When the block number
passes one era rounds, the reward is reduced by 20%.

See https://github.com/ethereumproject/ECIPs/blob/master/ECIPs/ECIP-1017.md

* Update rewards for uncle miners for ECIP1017

In the monetary policy, the rewards are changed from "up to 7/8 of the
reward" to "1/32 of the reward".

* Fix an off-by-one error in ECIP1017 era calculation

According to
https://github.com/ethereumproject/ECIPs/blob/master/ECIPs/ECIP-1017.md,
when in block number 5,000,000, it should still be in Era 1 (which in
our code `era == 0`). So we need to check whether the `rem` equals to
zero and act accordingly when calculating the era.

* `ecip1017_era_rounds` missing from EthashParams when run in build bot

* strip out ecip1017_eras_block_reward function and add unit test