Enable coloring of contours by different scalar array

[cquammen]

For datasets that have multiple scalar arrays, we want to be able to color the contour from one array by another array. Currently, one can color the contour by only label maps in child data sets. I plan to change the behavior to offer up only arrays available in the data source.

Related to #1405 in terms of how we will color contours by label maps.

[cquammen]

Do we want to keep the ability to color by child data sets, @cryos?

[cquammen]

We should consider separate data range controls for the color map applied to the contour. The range currently used is from the active scalar array shown in the histogram view. This range may be quite different from the range of the data array used to color the contour.

[cryos]

If the generated arrays become part of the data source, then I think the need to color by child data sets goes away. If we end of keeping them as children then we would want to retain the feature.

Agreed on looking at a separate control for the scalar array got coloring contours.