FIX SelectEpochs:  When saving,store bad channels as names, not indices
ENH mne_experiment.print_tree():  allow custom root, DOC
ENH mne_experiment:  add `add_bads` kwarg to more load_x methods
ENH mne_experiment:  store bad channel information with "{badch-key}" template key instead of (subject, experiment) tuple
ENH mne_experiment:  add **kwargs to __init__ for consistency with __repr__