WIP RF plot.brain:  use new PySurfer Brain features
STY data_obj
ENH plot.brain:  guess `smoothing_steps` based on src grade
API:  remove `split_label()` (added to mne)
FIX NDVar:  source space connectivity
FIX NDVar:  always copy() inherited info dicts
ENH NDVar:  indexing with boolean NDVar
ENH NDVar:   new methods: any, max, mean, min
ENH MneExperiment:  PySurfer plotting