Wallet Refactor

The wallet interface should now be compatible with exchanges. There has been a good amount of testing, especially considering that the TestComplexForking from the consensus set actually also makes sure that the forking passes all of the sanity checks in the wallet as well.

One unfortunate change is that creating a wallet now takes up to a full second (depending on the machine). I'm not sure where the bottleneck is. PublicKeysPerSeed has been set to 100 for now. I'm guess that 100 is not enough, and that 250+ will be necessary. I would like to be able to go much higher than that, but that might start to get resource intensive. The biggest concern is for renters and hosts, who will be making frequent new addresses. It's possible that they will be making their own seeds.

Compatibility with the old wallet files has not been added yet. Compatibility with siag files has not been added yet. Documentation is pretty sparse.

I promise I did not do all of this on August 7th. Github is confused.