Re-implement proper Unity support.

Somewhere in the transition from the original Ambiance theme to the Ambiant-MATE themes, Unity support became a bit lackluster. With the advent of projects like Ubuntu Unity Remix and the continued maintenance of Unity 7, it might be an idea to bring the Ambiant-MATE themes more in par with their original counterpart to provide more use outside of the MATE desktop. Most of the current errors are visible in the window decoration, but there are some other oddities (barely readable font in the Unity panel when the mixed Ambiant-MATE theme is selected, for instance.)

(Pictured: an example of the strange titlebars)

I believe that the bulk of these issues can be fixed by examining the difference between the gtk-widgets.css files in Ambiance, Radiance and the Ambiant-MATE themes.