def add_subgroup(label, &proc)
      columns = ActiveScaffold::DataStructures::ActionColumns.new
      columns.label = label
      columns.action = action
      columns.configure(&proc)
      exclude columns.collect_columns
      add columns
    end
def add_subgroup(label, &proc)
      columns = ActiveScaffold::DataStructures::ActionColumns.new
      columns.label = label
      columns.action = action
      columns.configure(&proc)
      exclude columns.collect_columns
      add columns
    end
nests a subgroup in the column set