title: Automatic label updates
body: <p>I'm using ChartJs for a small project in a daughnut form. Of course when you de-select a label the chart adjust itself, but I want that my numbers are automaticaly updated too.
  I put everything in % and I want that if a label is removed, it live updates itself.
  Here is my current code : </p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="false" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>var ctx = document.getElementById("myChart");
  var myChart = new Chart(ctx, {
    type: 'doughnut',
    data: {
      labels: [
        "Marche",
        "Course",
        "Natation",
        "Vélo"
      ],
      datasets: [{
        data: [65.45, 10, 10, 14.55],
        backgroundColor: [
          "#00ff00",
          "#008fb3",
          "#ff0000",
          "#ffff00",
        ],
        borderWidth: 1
      }]
    },
    options: {
      tooltips: {
        callbacks: {
          label: function(tooltipItem, data) {
            var allData = data.datasets[tooltipItem.datasetIndex].data;
            var tooltipLabel = data.labels[tooltipItem.index];
            var tooltipData = allData[tooltipItem.index];
            var total = 0;
            for (var i in allData) {
              total += allData[i];
            }
            var tooltipPercentage = Math.round((tooltipData / total) * 100);
            return tooltipLabel + ': ' + tooltipData + ' %';
          }
        }
      },
      title: {
        display: true,
        text: 'Récapitulatif des séances de sport',
        fontColor: "#000"
      },
  
      legend: {
        display: true,
        labels: {
          fontColor: '#000',
        }
  
      }
    }
  });</code></pre>
  <pre class="snippet-code-css lang-css prettyprint-override"><code>.graphsize {
    width: 500px;
    height: 500px;
    border: solid black 5px;
    border-radius: 15px;
  }
  body {
    margin-left: 27%;
    margin-right: 25%;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/2.4.0/Chart.js"&gt;&lt;/script&gt;
  &lt;div class="graphsize"&gt;
  
    &lt;canvas id="myChart"&gt;&lt;/canvas&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>I'm a beginner with this api so please explain me how to do this.</p>
  
  <p>Tristan</p>