Fix color scalarbar

@jcfr @fedorov @lassoan

ENH: Fixed color scalar bar by replacing vtkScalarBaractor with vtkPVScalarBarActor

Improvements:

* Color scalar bar was enhanced and the bugs were fixed by adding Paraview vtkPVScalarBarActor to module's logic
* Replaced vtkScalarBarActor with vtkPVScalarBarActor
* Made the logic sensitive to dicom volume. (for none dicom volumes the
 color scalar bar would occupy 100% of the view's width)
* Change the format of foreground volume and label opacities to percentage
(e.g. from 0.4 to 40%)