ENH: Add BatchUpdateThreshold to Model hierarchy logic

Only use batch processing for show/hide of model hierarchies if the
total number of nodes in the selected branch is larger than a given threshold.
STYLE: Update comment, fix indent and style in vtkMRMLScene
ENH: Update CTK to integrate Andras Lasso VTK connection optimization.

Andras Lasso (3):
      ENH: Use a hashmap to avoid linear search for existing vtk connections
      BUG: Fixed ctkVTKObjectEventsObserverPrivate::findConnection behavior for wildcards
      ENH: qvtkConnect and qvtkDisconnect performance improvement

Jean-Christophe Fillion-Robin (1):
      Merge branch 'vtkconnect-performance-improvement-consolidated'