ENH testnd:  duration based cluster correction
ENH mne_experiment:  add .next() method to move through field values
ENH mne_experiment:  more rejection options

- use `kind` entry as primary option
- allow "make" (made by the user but not with rejection GUI)
STY mne_experiment.list_files()
ENH mne_experiment:  add .make_raw() with some defaults
FIX SelectEpochs:  remove bad sensors from mean seg
ENH mne_experiment.make_epoch_selection():  automatically specify mad channels
ENH mne_experiment:  add make option to .get()
FIX/ENH SelectEpochs:  layout;  nplots arg, DOC
FIX wxterm:  load small files without known extension as plain text