TableView HeaderView autoresize

    override func viewDidLayoutSubviews() {
        super.viewDidLayoutSubviews()

        // resize header view
        if let headerView = tableView.tableHeaderView {
            let size = headerView.systemLayoutSizeFitting(UILayoutFittingCompressedSize)
            if headerView.frame.size.height != size.height {
                headerView.frame.size.height = size.height
                tableView.tableHeaderView = headerView
                tableView.layoutIfNeeded()
            }
        }
    }