Cleanup liquidation

[godsflaw]

Once the gem lands in the flipper, there is some real-world legal process that will result in repayment of the gem. We may want to create a authed interface, perhaps deal(), on the flipper that allows the DAI to be repaid and gives the gem to the person that repaid (probably the pause proxy in this case).

I haven't thought through the idea completely. I just wanted to write something down before I moved on to other things and forgot.