The constructor calls the GUISwarm's creation method, and then creates the model.
With GUI Swarms, it is necessary to follow the buildObjects/buildActions convention.
Activate the model and the display update schedule.
main is the class method called when a class is run. This is where everything starts
Note main is a class method, not an instance method. The ObserverSwarm does not yet exist.
Activate ourself in null. (Toplevel Swarms are activated in null.)