title: How to destroy gridstack before create new?
body: <p>I use single page app, I create 3 Gridstack in 3 pages.<br>
  If I open page one by one, the speed for resizing widget becomes slower for each page.<br>
  But, if I reload the page it works ok. </p>
  
  <p>I used Backbone's Router to open each page (not reload page).<br>
  This is my code:<br>
  Grid-satck.js</p>
  
  <pre><code>createGridStack: function(gridEl) {
          var options= {
              animate: true,
              width: 12,
              cell_height: 50,
              resizable: {
                  handles: "e, se, s, sw, w"
              }
          };
          $(gridEl).gridstack(options);
      }
  </code></pre>
  
  <p>template: div class='grid-stack'/></p>
  
  <p>HomePageLayout.js</p>
  
  <pre><code>return Backbone.Marionette.LayoutView.extend({
      template: "template",
      onShow: function() {
         createGridStack($(".grid-stack"));
         this.gridStack = $(gridStackEl).data('gridstack');
         this.gridStack.movable('.grid-stack-item', false);
         this.gridStack.resizable('.grid-stack-item', false);
      }
  })
  </code></pre>
  
  <p>ClientLayout.js</p>
  
  <pre><code>return Backbone.Marionette.LayoutView.extend({
      template: template,
      onShow: function() {
         createGridStack($(".grid-stack"));
         this.gridStack = $(gridStackEl).data('gridstack');
         this.gridStack.movable('.grid-stack-item', false);
         this.gridStack.resizable('.grid-stack-item', false);
      }
  })
  </code></pre>
  
  <p>LayoutSetting.js</p>
  
  <pre><code>return Backbone.Marionette.LayoutView.extend({
      template: "template",
      onShow: function() {
         createGridStack($(".grid-stack"));
         this.gridStack = $(gridStackEl).data('gridstack');
      }
  })
  </code></pre>