Merge topic 'fix_opacity_mapping' into pv-master

a5daf047 BUG: Fixed opacity mapping when scalar array is vtkUnsignedChar.
Merge remote-tracking branch 'pvvtk/pv-master' into HEAD

* pvvtk/pv-master:

Change-Id: Id18774d1fa6a7a8e2f0c4bfc886a6a997d962998