vtkSynchronizedTemplates3D was using a data member (ExecuteExtent)
to "communicate" between RequestUpdateExtent() and RequestData().
This made it impossible to call RequestUpdateExtent() from multiple
threads simulataneously even when using different input/outputs.
Changed such that vtkSynchronizedTemplates3D is using an entry
in the output information object instead. This allows calling from
multiple threads as long as the information object is specific to
each thread.

In the process, I also removed bunch of references to
vtkKitwareContourFilter, which no longer exists.

Change-Id: I67672ebc48546e320403a80cae98c787e9c2edbe