ENH: Consolidate ResliceMapper OpenGL code into SliceMapper.
The files vtkOpenGLImageResliceMapper was very similar to the file vtkOpenGLImageSliceMapper. After this change, the ResliceMapper delegates to the SliceMapper to avoid code duplication.
The files vtkOpenGLImageResliceMapper was very similar to the file vtkOpenGLImageSliceMapper. After this change, the ResliceMapper delegates to the SliceMapper to avoid code duplication.