Encryption itself is unchanged by this commit except that the key is now derived from the password only once. So it still uses SHA-256 for this.
The next step is changing this to a proper KDF, by changing the implementation of GenerateEncryptionKey and the TSetupEncryptionKey type.
Todo:
-Use a single random base nonce for all files
-Remove/replace various iscrypt use in .iss scripts
-Delete iscrypt.dll on updates
-Update help & whatsnew & web
-Rename TSetupSalt/TSetupNonce?
