SafeArea Top Constraint Setup, with Backwards Compatability

safeAreaTopAnchor.swift

/** Safe area for status bar dodging only. If you use NavigationBars, this won't help.
 */
let topConstraint: NSLayoutConstraint
if #available(iOS 11.0, *) {
    topConstraint = headerContainerView.topAnchor.constraint(equalTo: safeAreaLayoutGuide.topAnchor)
} else {
    let statusBarHeight = UIApplication.shared.statusBarFrame.height
    topConstraint = headerContainerView.topAnchor.constraint(equalTo: topAnchor, constant: statusBarHeight)
}