Add abiltiy to generate chaincodes from passpharses

Gives the ability to generate either Electrum or Armory chaincode / restore codes from a given passphrase, allowing you to have more than 1 brain wallet address to a given phrase.

All the usual caveats about bitcoin addresses generated from passwords apply, obviously.

One downside is that I wanted to use SHA512 so there wasn't any SHA256(SHA256()+??) expansion going on so the hex key could be easily calculated / verified outside of BW.