r20210217: temporary fix for rf nifti

This release aims to be used for testing RF nifti loading.
Old RF dicoms and nifti were based on a incomplete dataset, causing bad handling by dcm2niix.
The new niftis have been obtained running st_dicom_to_nifti over a complete set of 256 dicoms.
This is a temporary solution: The branch the release is based on will be removed once we acquire a smaller dataset at the MNI.