The heuristic did not handle DICOM series named "dwi_acq-(...)b0ref"
correctly - it placed them as "_sbref" into dwi/, while they should
have been "_epi" in func. These have an opposite phase encoding
direction to the main dwi acquisitions, and are intended for field map
correction.
This change assigns the correct folder and suffix to these files, and
adds dir-PA / dir-AP to the dwi and reference acquisitions. As a
result, QSIPrep should pick these up as field maps and apply
susceptibility distorsion correction.
