Double notification

[jacopoabramo]

While testing #32, I noticed that callbacks are invoked twice.

I tweaked micromanager_example.py and ran it via command line as:

python src\engine\exengine\micromanager_example.py

and got the following output:

Notification received: NotificationCategory.Data - DataCoordinates: {'time': 0}
Notification received: NotificationCategory.Data - DataCoordinates: {'time': 0}
Notification received: NotificationCategory.Data - DataCoordinates: {'time': 1}
Notification received: NotificationCategory.Data - DataCoordinates: {'time': 1}
Notification received: NotificationCategory.Data - DataCoordinates: {'time': 2}
Notification received: NotificationCategory.Data - DataCoordinates: {'time': 2}
Notification received: NotificationCategory.Data - DataCoordinates: {'time': 3}
Notification received: NotificationCategory.Data - DataCoordinates: {'time': 3}
Notification received: NotificationCategory.Data - DataCoordinates: {'time': 4}
Notification received: NotificationCategory.Data - DataCoordinates: {'time': 4}

Maybe the way I'm running the example is wrong though, I'm not sure.