vtkIceTSynchronizedRenderers and vtkEDLShading were not releasing graphics
resources when context was destroyed. That meant invalid graphics objects were
being used. When saving animations, screen is often resized and hence new
graphics context is created. That resulted in segfaults due to the use of bogus
graphics resources. Fixed that.

Change-Id: I186bc35984ceb1083f0d28cceecd7566bc8df643