Switch to gYFI time weighted voting power distribution

@DCinvestor @Dark @jimsox @ETH_Maximalist @dudesahn @Leo and @kazuya are having a similar conversation related to potential problems that could occur if a bad actor borrows YFI. We should consider consolidating the discussion to include everyone’s ideas.

Their discussion can be found at http://gov.yearn.fi/t/yfi-can-now-be-borrowed-to-participate-in-yearn-governance-via-aave/