title: Save image to photo album with datetime metadata
body: <p>I'm trying to use the metadata property in <code>writeImageDataToSavedPhotosAlbum</code> to save a GIF to the iPhone's photo album and add date/time metadata so that the saved GIF appears in a different place in the user's photo album instead of the default location at the end of the photo album.</p>
  
  <p>I've tried doing the following:</p>
  
  <pre><code>let metadata: [String: AnyObject]! = [kCGImagePropertyTIFFDictionary as String: 
      [kCGImagePropertyTIFFDateTime as String: dateTime!], 
      kCGImagePropertyExifDictionary as String: 
      [kCGImagePropertyExifDateTimeDigitized as String: dateTime!, 
      kCGImagePropertyExifDateTimeOriginal as String: dateTime!]]
  library.writeImageDataToSavedPhotosAlbum(data, metadata: metadata, completionBlock: completionBlock)
  </code></pre>
  
  <p>and the debug print for the metadata variable shows:</p>
  
  <pre><code>["{TIFF}": {
      DateTime = "2015:10:09 20:07:48";
  }, "{Exif}": {
      DateTimeDigitized = "2015:10:09 20:07:48";
      DateTimeOriginal = "2015:10:09 20:07:48";
  }]
  </code></pre>
  
  <p>However, it doesn't seem like setting the metadata worked because the GIF is still saved at the end of the photo album with the current timestamp instead of the timestamp that I'm trying to set.</p>