title: UICollectionView spacing margins
body: <p>I have a <code>UICollectionView</code> which shows photos. I have created the collectionview using <code>UICollectionViewFlowLayout</code>. It works good but I would like to have spacing on margins. Is it possible to do that using <code>UICollectionViewFlowLayout</code> or must I implement my own <code>UICollectionViewLayout</code>?</p>