showChart(timeseries) {
    timeseries.forEach(function(point) {
      point[0] = new Date(parseInt(point[0], 10));
    });
    var data = new google.visualization.DataTable();
    data.addColumn('date');
    data.addColumn('number');
    data.addRows(timeseries);
    var wrapper = new google.visualization.ChartWrapper({
      chartType: 'LineChart',
      dataTable: data,
      options: {
        title: 'Brightness over time',
        curveType: 'function',
        legend: {position: 'none'},
        titleTextStyle: {fontName: 'Roboto'}
      }
    });
    $('.panel .chart').show();
    var chartEl = $('.chart').get(0);
    wrapper.setContainerId(chartEl);
    wrapper.draw();
  }
Shows a chart with the given timeseries.
@param {Array<Array<number>>} timeseries The timeseries data
    to plot in the chart.