FIX Model:  include intercept in .df
TEST:  fix test_mne

create source spaces if they don’t exist
ENH stats:  add betas()
OPT opt:  _lm_betas
ENH plot.brain:  add plot.brain.annot()
RF MneExperiment.plot_parc():  use plot.brain.annot()
WIP STY:  reduce capitalized variable names
ENH GUI:  add Window Menu with Minimize and Zoom items