minor improvement to using the dune.fem.plotting function allowing to
simply write plot(div(uh)) without needing to also pass in a gridView, i.e., not needing to write plot(div(uh)),gridView=uh.gridView)
simply write plot(div(uh)) without needing to also pass in a gridView, i.e., not needing to write plot(div(uh)),gridView=uh.gridView)