refactor block reward calculators to params/

[meowsbits]

Migrated from: https://github.com/etclabscore/multi-geth-fork/issues/66 Original author: @meowsbits

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https://github.com/etclabscore/multi-geth/blob/feat/x-chainspec-types-and-tests/consensus/ethash/consensus.go#L547-L571

Logic should be in params/. The logic(s) are implementations of IP-defined parameters. And will keep keep all related logic centralized together.

rel #64

[iquidus]

to chain config or ethash config?

Ubiq migrated rewards to ethash config.

https://github.com/ubiq/go-ubiq/blob/master/params/config.go#L68 https://github.com/ubiq/go-ubiq/blob/master/consensus/ubqhash/consensus.go#L622

[ziogaschr]

@iquidus can we close this one?