define badge color directly

[Danielle Foré]

If we want to have badges in other parts of the UI (like in Slingshot or on Tabs/Switchers) we'll probably want to be able to define the badge color directly in the dock so that we can keep the color consistent.

I imagine we'll probably want to create some kind of Granite widget using Gtk.Overlay that we can put over just about any other Gtk element (buttons, icons, etc). So there we'll probably define a new style class in the theme like ".badge". Not sure if that's relevant information to how we might want to do this in the dock.