IOS: If notification is fired with date now or in the past, fire immediately

The Local Notifications plugin uses the function:
```m
[[UIApplication sharedApplication]
         scheduleLocalNotification:notification];
```
To schedule a notification. However, I was finding that it did not work reliably for notifications that you want to be displayed "right now"... This could happen, for instance, if you're doing background geolocation, and you want to display a local notification.

This commit looks at the fireDate for a notification, and if it is for this second, or in the past, then it will use the method presentLocalNotificationNow to display it.