ENH MneExperiment:  ADD .make_report_clusters()
ENH SourceSpace:  represent .parc as Factor
OPT connectivity:  use sorted array of [src, tgt]

Dimensions return connectivity as array instead of sparse matrix
ENH SourceSpace.connectivity():  ADD disconnect_parc option
ENH MneExperiment:  use `parc` for stc_ndvar()
WIP cdist