ormat time stamps for bottom of chart
   *                                             // you may use SmoothieChart.timeFormatter, or your own: function(date) { return ''; }
   *   scrollBackwards: false,                   // reverse the scroll direction of the chart
   *   horizontalLines: [],                      // [ { value: 0, color: '#ffffff', lineWidth: 1 } ]
   *   grid:
   *   {
   *     fillStyle: '#000000',                   // the background colour of the chart
   *     lineWidth: 1,            