Upgrade to Arc v58, Rinkeby contract addresses

[dkent600]

Resolves: #82

• upgrades to Arc v58, including particularly changes to reputation bootstrapping contracts
• adds contract addresses for rinkeby
• Arc.js migration script now maintains the Ganache contract addresses supplied by the DAOstack migration repo, meaning that the account addresses have changed as a result.
• ContributionReward.proposeContributionReward will now optionally take a proposal description that has already been hashed (and won't hash it). See ProposeContributionRewardParamsdescriptionIsHashed.
• unstubs stubbed-out GenesisProtocol scheme parameters.
• removes ContributionReward.ContributionProposal.contributionDescriptionHash

Breaking

• Ganache account addresses have changed.
• removes ContributionReward.ContributionProposal.contributionDescriptionHash