Change vow to split out accounting from auction logic

[hexonaut]

Similar to #241 this is designed to make the vow immutable going forward, but instead of using a proxy it splits things out into two contracts. Read the other PR for the reason why this is important. First step is to get this working same as before. After that we can fix things like the kiss(...) debt blocking bug.

WIP Tests are still failing and code is not complete.

Notes:

• Compared to the proxy vow this will require updating the liquidations to use the bow instead of the vow.
• Also, naming maybe sow is better than bow ? No reason for bow in particular it was just the first thing that came into my head.

[talbaneth]

Small note - dog.sol will need to change to use both vow and bow.
Also any UI/bot that integrates with flap (and flop) auctions will still rely on the bow address and will have to update each time it changes.