vtkSMProxy: track producers/consumers
Adding API to vtkSMProxy to track producers and consumers.
Also introducing vtkSMCommand
to maintain all events fired by
ServerManager. Makes it easier to define new events with names that make
more sense than reusing closet-matches from vtkCommand and arbitrarily
defining new ones.
Also includes other changes to resurrect old classes.
Edited by Utkarsh Ayachit