Allow gradient table to have more than 4 columns
Allow gradient table to have more than 4 columns

This is useful when the input gradient scheme contains additional
parameters - in our case, the phase-encode direction

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