Storage proofs

To the best of our knowledge, this finishes everything off. Everything at this point is supposed to work.

The environment I feel is in a pretty bad shape after this PR. Also a handful of functions in Siacore seem to be in pretty bad shape. I'm pretty certain we've got several minor race conditions, but I don't expect problems because we'll only be writing to the state every 10 minutes or so.

If we can get everything working and past 1000 blocks, we'll call it good enough. And then we can get to re-writing the ugly bits and expanding the test library.