title: Tracking upload progress in itemView
body: <p>I am developing an application with Marionette/Backbone.  The app needs to upload files over an AJAX call (have this working).  I want to give the user feedback on when they are able to select the uploaded file and proceed with modifying it.  I don't know what the best practice is for tracking the progress when I have a Model and ItemView for it.  I could put it in the attributes but as far as I know, all of the attributes will be saved into the database when it syncs to the server.  But the ItemView needs to be able to listen to the model as to when it is done, I just am unsure when and where to do that.</p>
  
  <p>I already have solved a more basic solution to this, but it needs to work within the Marionette/Backbone framework.</p>
  
  <p>Relevant part of ItemView</p>
  
  <pre><code>modelEvents: {
      'change': 'fieldsChanged'
  },
  
  fieldsChanged: function() {
      this.render();
  },
  </code></pre>