FIX is_datalist()
FIX mne_experiment:  error message
ENH/FIX UTS dim:  initialize with tmax instead of step (for better precision)
ENH/FIX load.fiff.evoked_ndvar(): lists of evoked

- find shared sensors
- check time points equal
- use UTS time dimension
ENH mne_experiment:  default n_jobs to 1