code: public static <T extends IItem & IExpandable> void selectAllSubItems(final FastAdapter adapter, T header, boolean select) {
          selectAllSubItems(adapter, header, select, false, null);
      }
docs: select or unselect all sub itmes underneath an expandable item
  
  @param adapter the adapter instance
  @param header  the header who's children should be selected or deselected
  @param select  the new selected state of the sub items