* use correct includes and inheritance

The global object can create an empty temporary local object that
can be bound to an element/stencil. This is closer to the
current dumux-stable implementation and still allows to switch
between global caching (for smaller problems where memory is not an issue)
and local caching (variables are precomputed for each element assemble temporarily)

Works for cc and box (in 2d). Box needs some performance improvement,
probably when creating the box geometries. But also other parts
might be possbile to optimize.

We iterate over all scvs of a fvElementGeometry like this
for (const auto& scv : scvs(fvGeometry))
This is closer to the way we speak "For each scv in all scvs of the fvElementGeometry do..."
and analogously to how we iterate over elements of a gridView.

The fvGeometryVector builds all sub control volumes, sub control
volume faces and fvGeometries; where the fvGeometries are merely
providing iterators over scvs and scvfs of an element.