[ticket/11103] Make sure notifications are marked read when clicking them

How do we do this? If an item is unread, the URL to view that item will
be the URL to mark it as read (index.php?mark_notification=$id). When the
URL is visited it marks the item as read and redirects them to the correct
URL for the item.

If the item is read, the URL is directly to the item.

Prettify the html output

PHPBB-11103

phpBB/includes/notification/manager.php

@@ -165,7 +165,7 @@ class phpbb_notification_manager
 			}
 			$load_special[$row['item_type']] = array_merge($load_special[$row['item_type']], $notification->get_load_special());
 
-			$notifications[] = $notification;
+			$notifications[$row['notification_id']] = $notification;
 		}
 
 		$this->load_users($user_ids);