title: Margins around cell like in Android GridLayout
body: <p>In Android it's easy to create a grid list with the next margins:</p>
  
  <p><a href="https://i.stack.imgur.com/EnG6s.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/EnG6s.png" alt="enter image description here"></a></p>
  
  <p>I found this solution for iOS but it doesn't add margins between cell and parent view, only between cells</p>
  
  <pre><code>let itemSpacing: CGFloat = 3
  let itemsInOneLine: CGFloat = 2
  flow.sectionInset = UIEdgeInsets(top: 0, left: 0, bottom: 0, right: 0)
  let width = UIScreen.main.bounds.size.width - itemSpacing * CGFloat(itemsInOneLine - 1) //collectionView.frame.width is the same as  UIScreen.main.bounds.size.width here.
  flow.itemSize = CGSize(width: floor(width/itemsInOneLine), height: width/itemsInOneLine)
  flow.minimumInteritemSpacing = 3
  flow.minimumLineSpacing = 3
  </code></pre>
  
  <p><a href="https://i.stack.imgur.com/JsOn0.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/JsOn0.png" alt="enter image description here"></a></p>
  
  <p>How can I solve it?</p>
  
  <p>P.S. I don't want to hardcode anything, so it should work ok for all iPhone/iPad devices</p>