BUG #13809. Release graphics resources cleanly.

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
Merge topic '13809_fix_edl_segfault' into next

f63737a BUG #13809. Release graphics resources cleanly.