title: Swift - Parse Check if PFFile is cached
body: <p>Considering I'm using PFImageViews, with caching enabled, I would like to know if there's a way to determine whether an image has already been downloaded or not.</p>
  
  <p>All in all, I want to say:</p>
  
  <pre><code>if imageAlreadyDownloaded {
      ...
  }
  else {
      ...
  }
  </code></pre>
  
  <p>Is it possible?</p>