Memory leaks

[phcerdan]

Opening the module without any data loaded, then perform no action, and closing slicer, produces a memory leak in vtkCollection.

Slicer closing print messages:

Switch to module:  ""
Switch to module:  ""
vtkDebugLeaks has detected LEAKS!
Class "vtkCollection" has 1 instance still around.

If something more useful is done, for example, creating three planes and clip, this is the result:

Switch to module:  ""
ctkSliderWidget::setSingleStep()  6.71768 is out of bounds. 58.0057 64.7234 61.3645
ctkSliderWidget::setSingleStep()  6.71768 is out of bounds. 58.0057 64.7234 61.3645
ctkSliderWidget::setSingleStep()  6.71768 is out of bounds. 58.0057 64.7234 61.3645
ctkSliderWidget::setSingleStep()  6.71768 is out of bounds. 58.0057 64.7234 61.3645
Switch to module:  ""
vtkDebugLeaks has detected LEAKS!
Class "vtkCollection" has 4 instances still around.
Class "vtkObserverManager" has 1 instance still around.
Class "vtkIntArray" has 3 instances still around.
Class "vtkMRMLModelNode" has 1 instance still around.
Class "vtkTagTable" has 1 instance still around.
Class "vtkCommand or subclass" has 3 instances still around.
Class "9vtkBufferIiE" has 3 instances still around.