Use global index sets by the dune-parmg module

This MR contains most of the changes of !22 (closed) , with some extra cleanup.

dune/gfe/parallel/globalmapper.hh

+#ifndef DUNE_GFE_PARALLEL_GLOBALMAPPER_HH
+#define DUNE_GFE_PARALLEL_GLOBALMAPPER_HH
+
+#if HAVE_DUNE_PARMG
+#include <dune/parmg/parallel/dofmap.hh>
+#include <dune/parmg/parallel/globaldofindex.hh>
+#include <dune/parmg/parallel/datahandle.hh>
+#endif
+
+namespace Dune {
+
+  template <class Basis>
+  class GlobalMapper
+  {
+  public:
+    using GridView = typename Basis::GridView;
+
+    /** \brief The integer number type used for indices */
+    using Index = typename GridView::IndexSet::IndexType;
+#if HAVE_DUNE_PARMG
+    typedef Dune::ParMG::EntitiesToDofsMap<Basis> DofMap;
+    typedef Dune::ParMG::EntityMasterRank<typename Basis::GridView> Master;
+    typedef std::vector<char> DofMaster;
+
+    GlobalMapper(const GridView& gridView_)
+    {
+      Basis b = gridView_;
+      DofMap dofmap = Dune::ParMG::entitiesToDofsMap(&b);
+      Master m = Dune::ParMG::entityMasterRank(gridView_, [&](int, int codim) -> bool {
+              return dofmap.codimSet().test(codim);
+            });
+      DofMaster dofmaster = Dune::ParMG::dofMaster(b, m);
+
+      coarseGlobalDof_ = globalDof(b,m, dofmap);
+
+      // total number of degrees of freedom
+      size_ = coarseGlobalDof_.size;
+    }
+#else
+    GlobalMapper(const GridView& gridView_)
+    {
+      // Total number of degrees of freedom
+      size_ = gridView.size();
+    }
+#endif
+
+    /** \brief Given a local index, retrieve its index globally unique over all processes. */
+    Index index(const int& localIndex) const {
+#if HAVE_DUNE_PARMG
+      return coarseGlobalDof_.globalDof[localIndex];
+#else
+      return localIndex;
+#endif
+    }
+
+    std::size_t size() const
+    {
+      return size_;
+    }
+
+#if HAVE_DUNE_PARMG
+    ParMG::GlobalDof coarseGlobalDof_;
+#endif
+
+    std::size_t size_;
+  };
+
+}
+#endif   // DUNE_GFE_PARALLEL_GLOBALMAPPER_HH