VTK: some infrastructure work to support writing of vector fields

- the constructor of VtkMultiWriter now expects a grid view as first
  argument. unfortunately the old API cannot be kept around with this
  change.
- as a follow up beginWrite() does not need the grid view as an
  argument anymore
- if the grid has been changed during two time steps, the new method
  gridChanged() must be called before beginWrite() is called

examples/tutorialproblem_coupled.hh

@@ -154,8 +154,9 @@ public:
      */
     bool shouldWriteOutput() const /*@\label{tutorial-coupled:output}@*/
     {
-        return this->timeManager().timeStepIndex() > 0 &&
-        (this->timeManager().timeStepIndex() % 1 == 0);
+        return 
+            this->timeManager().timeStepIndex() > 0 &&
+            (this->timeManager().timeStepIndex() % 1 == 0);
     }
 
     // Return the temperature within a finite volume. We use constant