iOS: Update collection view layout for a better looking grid

[yoshisuga]

The Games list screen had some wasted space in the middle, where the items would be pinned to the leading and trailing edges of the collection view.

Updated to use the UICollectionView compositional layout API to better support a grid layout. It also supports iPad using the trait collections/size class. This API however requires iOS 13. (PR: https://github.com/jpd002/Play-Dependencies/pull/29)

Also updated the collection view cell to use auto layout constraints for the label.