Forward below- and above-range colors to internal vtkLookupTable

Also simplified overriding of SetNanColor by using the "using" keyword
to unhide methods rather than redefining them and calling the
superclass versions.

Change-Id: Ief8e262b51f05f7e55bd06acdc87d3c234cacf45
Avoid overriding hidden methods with the "using" keyword

Change-Id: I70140e0ba7a7a94437a9bd50eee72fd6734aaa5e
Updated computation of scalar table and texture coordinates

The new computation takes into account the below- and above-range
colors which are stored in the table as the first and last texel,
respectively.

Change-Id: I0a5c0846e47ca8176ffb96da1b7e2dc511a56ccd
Use the correct colors for colors above or below range

Change-Id: I8049318e129723615b60f20542f902004ba9fcc7
Use black if out-of-range colors aren't used

Change-Id: I8fe5e10683a74d180e2501aad7007d363dca3a35
Fix function that returns color from index

Change-Id: I98b13452124a149af7153990e8051379feeb6953
Fixed setting of out-or-range colors passed to color lookup function

Change-Id: Iffb29a44acfdcbe7d766cbece5da2f7d8a06dee0