title: Fetch PHAssets that don't belong to any PHAssetCollection
body: <p>Is it possible to fetch all <code>PHAsset</code>s that don't belong to any <code>PHAssetColletion</code>? Basically what I want to achieve is to get all photos that are not sorted to any album.</p>
  
  <p>I know I can do this:</p>
  
  <pre><code>let photos = PHAsset.fetchAssets(with: PHFetchOptions())
  var photosWithoutAlbum: [PHAsset] = []
  photos.enumerateObjects({
      asset, index, stop in
      let albums = PHAssetCollection.fetchAssetCollectionsContaining(asset, with: .album, options: PHFetchOptions())
      if albums.count == 0 {
          photosWithoutAlbum.append(asset)
      }
  })
  </code></pre>
  
  <p>But maybe there is a better/faster way using <code>PHFetchOptions</code> or different fetch method?</p>