Created attachment 351328 [details] [review]
gs-shell: use headerbar in toolbar-mode in Unity

In Gnome-Software the headerbar in unity is used as a toolbar, but without applying the proper .primary-toolbar class, which leads to make impossible to use Unity themes properly in other environments (as GS) as they try to apply a toolbar-like theme to any headerbar that is not a titlebar (which might be in cases in other apps, where custom headerbar widgets are heavily used).