title: Detect monitor when system messages and notifications are displayed and dismissed?
body: <p>Sometimes an iOS system message will be displayed and interrupt an app. For example, a privacy system message might ask for access to a photo album or to use the microphone, or a system message might display a notification such as low battery.</p>
  
  <p>What techniques can be used for iOS7/8/9 in Swift that detect and monitor when a system message or notification is displayed and also when it is dismissed?</p>