PTSPipelineViewer : Restrict ParentIDs to pipeline proxies

Previously, vtkPipelineElement::GetParentIDs() will return ids for all proxies used by this including subproxies. We want to skip those from the pipeline connectivity, so we filter by the sources registration group which is used in vtkParaViewPipelineController when registering any pipeline proxy.

This fixes the issue of the clip filter now showing up in pipeline in the demo