added a new class "Component".

currently, all windows inside our tooling are derived directly from Gtk.Bin.
this makes it impossible to add new common stuff (like an IntPtr constructor...) to them consistently.
we anyway wanted to do this.
now the time has come.
"Component" currently is a simple child class of Gtk.Bin, from which you should derive your windows inside the tooling.
The name has been chosen in analogy to IComponent, IComponentInteract etc.