issue #173. Control items text can be configured

Usage]
  // multiBar Chart
  chart.controlsData({
      groupedName: 'Type A',
      stackedName: 'Type B'
  });

  // Area Chart
  chart.controlsData({
      stackedName: 'Type A',
      streamName: 'Type B',
      expandedName: 'Type C',
  });