title: How to remove one specific object from selection
body: <p>I'm trying to make a restriction: when a group of objects is selected, some specific object must not be included in the selection.</p>
  <p>F.e. we create 3 rectangles. If we select the group and the red one is inside of it, it must be removed from selection:</p>
  <pre><code>function addRect(){
      var redRect = new fabric.Rect({
          left: 50,
          top: 50,
          fill: 'red',
          width: 50,
          height: 50
      });
  
      var greenRect = new fabric.Rect({
          left: 100,
          top: 100,
          fill: 'green',
          width: 50,
          height: 50
      });
  
      var blueRect = new fabric.Rect({
          left: 150,
          top: 150,
          fill: 'blue',
          width: 50,
          height: 50
      });
  
      canvas.add(redRect);
      canvas.add(greenRect);
      canvas.add(blueRect);
  }
  
  
  function createCanvas(id){
      canvas = new fabric.Canvas(id);
      addRect();
  
      canvas.on('selection:created', function(e) {
          for (var i = 0; i &lt; canvas.getActiveObjects().length; i++) {
              if(canvas.getActiveObjects()[i].fill == &quot;red&quot;){
                  //somehow remove the red one from selection
              };
          }
      });
  
      return canvas;
  }
  </code></pre>
  <p>discardActiveObject() will remove the whole selection.</p>
  <p>&quot;selected = false&quot; also doesn't work.</p>
  <p>Any ideas?</p>