hgk: in popups, replace labels with window titles Replace labels with window titles. That also requires to change grid placement manager settings to compensate padding which used to be applied to now non-existent labels.

hgk: update backgroud colour when Ttk is available Ttk doesn't automatically set up Tk colour palette. Because of that, Ttk controls look differently when used together with old Tk controls. When we use Ttk controls, we first query if we have any setting for the client background, and if we do, we update Tk palette as well.