Cortical Structures do not (yet) have Laterality information

[adswa]

I think this is ultimately was the cause of #5: Currently, for the creation of the nidm graph with add_seg_data(), anatomical structures are expected to have a laterality associated with them. This is true for the anatomical terms in aseg.stat files, but not for cortical structures in aparc.stat files (see the second sheet in ReproNimCDEs.xlsx).
In #11, I mitigate the problem suboptimally by just specifying that the laterality is undefined. Given my lack of freesurfer experience, I don't know whether we should add any information about laterality to these anatomical terms (that would need to be done in the spreadsheet) or have that field empty.