Prop 211: Reduce collateral factor for USYC 90% -> 85% and FBILL and IFBILL from 99% -> 90%

This proposal is a follow up to #206 and brings the USYC rate down to 85%, compatible with other stables in the lending market. It also brings down the FBILL and IFBILL rates which where not changed in the first proposal becuase outdated contract addresses where provided in the proposal.