FIX load.tsv():  empty string cells
FIX testnd:  find clusters without permutation
ENH MneExperiment:  ADD `.plot_roi_tc()` and `.plot_roi_tc_subject()`
ENH MneExperiment:  ADD ttest movies
ENH MneExperiment:  add `._model_order = []` attribute to specify order of factors in models
ENH MneExperiment:  epoch event selection

Select events for epochs based on expression rather than than `stimvar` and `stim`
ENH MneExperiment:  simplify epoch description

 - only use `epoch` and `rej` in templates
 - move `pad` into epoch specification dict
 - rename epoch selection and evoked dirs
ENH Experiment state management

store_state() an restore_state() methods
ENH MneExperiment:  allow initialization without proper root/subejcts
STY:  MneExperiment
ENH plot.brain (API):  use new PySurfer features

 - use PySurfer Brain as top level return value
 - guess `smoothing_steps` based on src grade
 - ADD plot.brain.cluster()
ENH MneExperiment:  reorganize labels

 - use different files:
	 - annot-file (Freesurfer *.annot)
	 - parc-file (pickled dictionary of label objects)
 - specify labels as string, no `label` state entry
 - Label plots
ENH: FIX for Freesurfer's mri_surf2surf
API utils:  remove `split_label()` (added to mne)
ENH MneExperiment:  use precomputed morph_matrix for morphing STCs
API MneExperiment:  default value for `inv`
WIP MneExperiment:  perform label sign flip for fixed source estimates
STY:  eellab imports * from lab
ENH:  add `labels_from_clusters()`
WIP labels_from_cluster:  NEED proper smooth values