Image::Filter::Smooth: allow use of types other than float
Image::Filter::Smooth: allow use of types other than float

This is useful to allow operation on e.g. complex types

MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3,MRtrix3/mrtrix3