Automatically unlock SEDs during boot
This is the first pass for unlocking SED drives at boot using passwords that can be saved via the GUI.
The passwords are stored encrypted in the database and are obfuscated via the GUI and API, however anyone with access to the database and the encryption key can decrypt the passwords.
Second pass is giving FreeNAs the ability to talk to a keyserver to unlock SED drives, that pull request will come later.
There is one deficiency in this pull request, if a drive with a password is modified unless the password is entered again the password will be removed. I need to talk to William about the best way to fix that, as the paradigm for "keep the existing field if the to be saved field is blank" doesn't exist in FreeNAS yet to my knowledge. (There's places other than SEDs this could be used IMO)