title: Change:position event for every cell in the paper using joint.js
body: <p>By clicking on a blank space of the paper a new cell will be added:</p>
  
  <pre><code>paper.on({
      'blank:pointerdblclick': function(event, x, y) {
          var rect = new joint.shapes.app.Standard({
              position: { x: x, y: y },
              size: { width: 100, height: 80 },
          });
  
          graph.addCell(rect);
  
          rect.on('change:position', function() {
              paper.fitToContent();
          });
      }
  });
  </code></pre>
  
  <p>But as the <code>change:position</code> event is set in the <code>blank:pointerdblclick</code> event, it just fires for new elements. But it should be set for all cells exisiting for this paper.
  So for moving of any cell on the paper the fitToContent()-function should be done...</p>
  
  <p>How do I do that?</p>
  
  <p>P.S.: The standard-element is defined like this:</p>
  
  <pre><code>joint.shapes.app.Standard = joint.shapes.basic.Generic.extend({
      markup: '&lt;rect/&gt;&lt;circle class="port-top"/&gt;&lt;circle class="port-bottom"/&gt;&lt;circle class="port-right"/&gt;&lt;circle class="port-left"/&gt;&lt;text/&gt;', 
      defaults: joint.util.deepSupplement({
          type: 'app.Standard',
          attrs: {
              ...
          }
      }, joint.shapes.basic.Generic.prototype.defaults)
  });
  </code></pre>