public RhythmGroup addOverlays(Collection<RhythmOverlay> overlays){
  mOverlays.addAll(overlays);
  if (mCurrentOverlayIndex == NO_OVERLAY) {
    selectOverlay(0);
  }
  return this;
}

public RhythmGroup addOverlays ( Collection < RhythmOverlay > overlays ) { mOverlays . addAll ( overlays ) ; if ( mCurrentOverlayIndex == NO_OVERLAY ) { selectOverlay ( 0 ) ; } return this ; }
add multiple rhythm overlays to this group
