Staging

[0xfornax]

• Fixed a zero ERC-20 transfer (when there is no gas compensation)
• Allow users to select which assets to claim from the Stability Pool
• New price feed with fallback logic
• When fully repaying debt, fix the current flow where users needed to pay the entire fee and receive a bit back. Now users only pay the proportional fee.
• We assume the FeeCollector would be whitelisted on the DebtToken contract to be able to burn excess GRAI from the previous item (we initially mint the entire fee - for the case users never repay - but once they do repay we can burn the excess).