public func collectionView(_ collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, sizeForItemAt indexPath: IndexPath) -> CGSize {
let numberOfColumns : CGFloat = 2
let width = collectionView.frame.size.width
let xInsects : CGFloat = 10
let cellSpacing : CGFloat = 5
return CGSize(width: (width / numberOfColumns) - (xInsects + cellSpacing), height: (width / numberOfColumns) - (xInsects + cellSpacing))
}