add flag to compute brainscore grouped by some neuroid coordinate or some sample coordinate, e.g., in RSA/CKA IdentityMaps

[aalok-sathe]

add split coords on sampleid and neuroid to brainscore scoring function to e.g., get 1 score per sub-experiment in the sampleid case or 1 RSA/CKA score per participant over voxels in the neuroid case.