FIX Layout:  for `w` and `ncol` parameters
FIX testnd:  `.diff_cl` in cluster t-test diff (make plot with overlay instead of 2 plots)
API load.brainvision.events():  Dataset entry `event_ID` -> `eventID` for consistency
FIX table.frequencies():  Var name should be str, hence use `cellname(cell)` instead of `cell`