STY MneExperiment.make_besa_evt()
STY:  eellab imports * from lab
ENH fmtxt:  `Section.add_image_figure()` allow adding image from existing file
ENH NDVar:  implement `Dimension.__eq__()`; check dimension when using NDVar index
STY fmtxt
STY EXA:  replace `eelbrain.eellab` with `eelbrain.lab`
WIP MneExperiment:  perform label sign flip for fixed source estimates
WIP: ENH:  add `labels_from_clusters()` (NEED proper smooth values)
ENH NDVar:  make boolean NDVar from comparison