Add function to return the order of an AnalyticDiscreteFunction

dune/curvedgrid/gridfunctions/analyticdiscretefunction.hh

@@ -265,6 +265,12 @@ public:
     return f_;
   }
 
+  /// \brief obtain the order
+  const int order () const
+  {
+    return order_;
+  }
+
 private:
   Functor f_;
   int order_;