Handling of cerebellum in some new parcellations

[Lestropie]

Some of the new parcellations in dev do not include cerebellar parcellation. Some also require a greater radial search distance due to incomplete GM coverage. Combining these two would mean that streamlines terminating in the cerebellum may be erroneously assigned to the most proximal cortical parcel.

This could be fixed by explicitly adding the cerebellar hemispheres into the parcellation, generating the connectome, then erasing the corresponding rows / columns from the matrix.