Extract GlobalPosition from Grid

There are many places where the global position type is locally defined as:

using GlobalPosition = Dune::FieldVector<Scalar, dimWorld>;

We maybe should think about extracting it from the Element (i.e. Element::Geometry::GlobalCoordinate) or from the sub-control volumes and sub-control volume faces (which itself should have been given the type extracted from the grid).

This is especially important when Scalar and ctype are not the same.