Removing Dependency on VolumeDataContainer to get the data array. It is
only important to get a generic DataContainer.
Fixing issue in code when writing the Xdmf file where the <Grid> tag would not get opened in the final Xdmf file if Vertices, Edges or Faces were missing causing invalid XML to be generated. We now open the tag at the minimum and write a short error message enclosed in XML comment tags in case something was not able to be written.