Make vtkScalarsToColorsPainter respect ScalarMaterialMode.

ScalarMaterialMode set on the vtkMapper was totally ignored by
vtkScalarsToColorsPainter. This fixes that. Also added a test that tests
the various configurations available for ScalarMaterialMode and
InterpolateScalarsBeforeMapping.

Change-Id: I9c0598db320534c0705f811e7e75ab7e21a47f08
Merge topic 'fix_scalar_material_mode' into master

f21207c1 Make vtkScalarsToColorsPainter respect ScalarMaterialMode.