* Add randomness contract support to Authority Round.
Changes have been cherry-picked from poanetwork's aura-pos branch.
Most of the work has been done by @mbr.
* Address review comments for randomness contract.
Co-Authored-By: David <dvdplm@gmail.com>
* Rename revealSecret to revealNumber
* Update Randomness contract bytecode
* Use H256, rename secret to random number.
* Use get_commit_and_cipher
* Clean up Miner::prepare_block.
* Remove is_reveal_phase call.
* Add more comments, require randomness contract map.
* Simplify run_randomness_phase
* Address review comments.
* Remove Client::transact_contract.
