fix user form field order and autocompletion

Storing passwords by browser breaks because the username field is not just before password. Also, editing your profile (or another user's) fills in one of the password fields with your own (on Firefox). This is annoying when editing.

This fixes these problems.

Side-effect: when updating your password in your profile, the browser does not offer anymore to remember your password (will happen when you login next with your new password). This may be solved by javascript removing the `autocomplete=off` property on form submission when the password was set. This is left as something for the future.