Admin UI: Show the OK button in the header of the Dialog window too

[jacobwod]

Because of the bugginess of current Admin UI, there are some scenarios where an important OK button can become invisible, and hence unclickable, for the user.

A solution for those cases is having the OK button to appear both in top and bottom of the Dialog inside Admin UI.

Note: the code is such a bad condition that it needs a solid rewrite, from scratch. I'm not doing it now, but rather focus on fixing the issue for those users and organisations that have been complaining about this.