Changed focus to better passphrase strength.

Removed per-stage passphrases, it is far more secure to have one very long
passphrase rather than specify multiple shorter ones that can be verified
separately.

Removed scrypt key derivation as key derivation is not as important
as using a strong passphrase to begin with.

Fixed the stages to an AES pass followed by a Blowfish pass.
They use different salts to generate the pbkdf2 derived keys.