UI: Deactivate ok button until password fields are filled in

-UI: when you change the password, you get the "password change successful" notification. The OK button is active after this, it should not be until you type new things in again.

the password dialog OK button should only be available once you have entered a password, new password, and confirmation.

(from redmine: created on 2014-11-24, closed on 2016-05-04)