ENH: slicer.util - Add convenience methods resetThreeDViews/resetSliceViews

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22854 3bd1e089-480b-0410-8dfb-8563597acbee
ENH: slicer.util - Add VTKObservationMixin python convenience class

This class provides a convenience interface to keep track of VTK
observations.

Assuming you have a class Foo already deriving from class Bar, you could
do:

class Foo(Bar, VTKObservationMixin):
  def __init__(self):
    super(Foo, self).__init__()

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22855 3bd1e089-480b-0410-8dfb-8563597acbee