Issued Shipment Manager Class - concrete ShipmentManager for issuedShipments.

Manager Classes in this context should do the bridge between the controllers and the services exposing only the necessary api to the controllers while encapsulating all business logic.

All Manager Classes should be singletons.

This complete separation of concerts is very beneficial for 2 reasons:

• Allows for testing since there's no browser dependent code (i think) since the DSUStorage can be 'mocked'
• Allows for different controllers access different business logic when necessary (while benefiting from the singleton behaviour)