Rather than speculatively compute unique values on every array
(before bug 13524) or on every active scalar (after bug 13524),
compute prominent values on demand when the color scale dialog is
actuated.

This is achieved by moving distinct-value detection out of the
`vtkPVArrayInformation` class and into its own `vtkPVInformation`
subclass named `vtkPVProminentValuesInformation`, which is fetched
on demand by the color scale editor.

This commit bumps the version of VTK used by ParaView so that
the updated prominent value detection is included.

Change-Id: I9b0eda74dfcb4faab775060d7b3c60a325597534