population template: some fixes to initialisation. reduced FOV of average space if possible
population template: some fixes to initialisation. reduced FOV of average space if possible

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