Adding basic wallets to Sia

Added disk-based wallets to Sia. Wallets are loaded from disk and saved to disk. Scripts can be loaded into and saved from wallets. There is support in the infrastructure for scripts up to 1mb in length, but currently no way to expand the size of scripts, meaning preliminary scripts will need to be under 1kb.

Changed bootstrapping so that the bootstrap gives himself a wallet
Did not change synchronization so that new hosts download new wallets.

Changed quorum.Status() to print an overview of all wallets stored on disk.

Added a few functions to siacrypto, I've now realized that siacrypto needs some changes to the way it does error checking. No eta on those changes, but probably sooner rather than later.
Skipped part of a test in signatures.go for short testing. Test remains in long testing.
uh...

wallets will probably wind up somewhere in the home folder, but during development, why not just use a relative path?