private void showOverlay(Region overlay, boolean blocking) {
    showOverlay(model.getOverlays().get(overlay), blocking);
  }
Makes the {@code overlay} visible, along with its {@code glassPane}.

@param overlay to be shown
@param blocking if false, will make {@code overlay} hide, if its {@code glassPane} was clicked
workbenchfx-core/src/main/java/com/dlsc/workbenchfx/view/WorkbenchPresenter.java