Add autocomplete attribute to some password fields

I was finding that my browser was auto-completing the first password field on my edit member account page, resulting in a password match failure if the password fields were left as is.

To prevent that, this commit sets the `autocomplete` attribute to `off` when `$mode` is not `login`. (The login form's password field has `autocomplete` set to `on`, meaning a member's browser can still pre-fill it if they have chosen to save their password.)