Made the demo project support iPad and silenced two warnings with Xcode 12.5 and Swift 5.4

[kaishin-r]

Here comes a crash on iPad and two warnings with Xcode 12.5 and Swift 5.4. This PR fixes these.

• Crash
  • The modalPresentationStyle of a UIAlertController with this style is UIModalPresentationPopover. You must provide location information for this popover through the alert controller's popoverPresentationController. You must provide either a sourceView and sourceRect or a barButtonItem. If this information is not known when you present the alert controller, you may provide it in the UIPopoverPresentationControllerDelegate method -prepareForPopoverPresentation.'
• Warnings
  • Using 'class' keyword for protocol inheritance is deprecated; use 'AnyObject' instead

[ivanvorobei]

Thanks!