ENH mne_experiment.label_events(): add T and SOA
FIX: plot.brain.stc._show_hemi()

Run only if visibility changes.
UPDATE plot.brain set_time -> PySurfer (#34)
ENH: mne_experiment.get_inv()

Add loose and fixed option
ENH: mne_experiment evoked pipeline

- make_evoked()
- load_evoked()
- add_evoked_stc()
cleanup/DOC
ENH: label pipeline