Dispose of toolbox when workspace is disposed.

demos/maxBlocks/index.html

@@ -81,7 +81,8 @@
   <script>
     var workspace = Blockly.inject('blocklyDiv',
         {media: '../../media/',
-         maxBlocks: 5, toolbox: document.getElementById('toolbox')});
+         maxBlocks: 5,
+         toolbox: document.getElementById('toolbox')});
 
     function onchange() {
       document.getElementById('capacity').innerHTML = workspace.remainingCapacity();