Adding stream support to various readers

vtkResourceStream can now be encapsulated into a std::streambuf using vtkResourceStream::ToStreambuf().

Stream support have been added to:

• vtkSTLReader

• vtkPTSReader

• vtkHDFReader (prefer memory stream)

• vtkCityGMLReader (prefer memory stream)

• vtkOpenVDBReader

• vtkDICOMImageReader

In that context the following protected methods are now private/removed:

• vtkSTLReader::ReadBinarySTL

• vtkSTLReader::ReadASCIISTL

• vtkSTLReader::GetSTLFileType