Allow const std::vector<vtkSmartPointer<T>> in Python

This commit is a follow-up of 8b3e3388 (Allow std::vector<vtkSmartPointer> in Python) to support wrapping custom classes with function like the following to be wrapped:

class vtkSegmentationCore_EXPORT vtkSegmentationConverterFactory : public vtkObject
{
public:
  typedef std::vector< vtkSmartPointer<vtkSegmentationConverterRule> > RuleListType;

  [...]

  const RuleListType& GetConverterRules();

  [...]
};

class vtkSegmentationCore_EXPORT vtkSegmentationConverterRule : public vtkObject
{
   [...]
};