Add per-block color support to vtkCompositePainter

This adds support for per-block coloring to vtkCompositePainter.

Change-Id: I4f357107c06c565ad5878501e573b8e3b9c0668c
Merge topic 'multi-block-color-support' into master

e43e157d Add per-block color support to vtkCompositePainter