ENH: Adds background color option to VTKViewer class

Adds background color option to VTKViewer class which
internally calls vtkRenderer
Status Job ID Name Coverage
  External
passed cdash

passed ghostflow-branch-check-master

passed ghostflow-commit-check

passed imstk-marvin-windows-shared-debug+msvc2013+omni

00:02:43

passed imstk-marvin-windows-shared-release+msvc2013+omni

00:00:16

passed imstk-norkit-osx-shared-debug

00:00:45

passed imstk-norkit-osx-shared-release

00:00:19

running imstk-requiem-linux-shared-debug

21022:44:32

running imstk-requiem-linux-shared-release

21022:44:29