Support image direction in vtkImageResliceMapper

These changes allow vtkImageResliceMapper to give correct results for oriented input images (that is, when the Direction isn't the identity matrix). The vtkImageSliceMapper already supported these oriented images.

At the same time, the mapper was reformulated so that it now uses the new vtkImageReslice::SetOutputDirection() method instead of using vtkImageReslice::SetResliceAxes().