Notifications: Make them work in debug mode

Fix #4274.

Only the app needs MXUIKitBackgroundModeHandler.

Config/AppConfiguration.swift

@@ -44,6 +44,9 @@ class AppConfiguration: CommonConfiguration {
         // Each room member will be considered as a potential contact.
         MXKContactManager.shared().contactManagerMXRoomSource = MXKContactManagerMXRoomSource.all
         
+        // Use UIKit BackgroundTask for handling background tasks in the SDK
+        MXSDKOptions.sharedInstance().backgroundModeHandler = MXUIKitBackgroundModeHandler()
+        
         // Enable key backup on app
         MXSDKOptions.sharedInstance().enableKeyBackupWhenStartingMXCrypto = true
     }