This method is used to paint this JPanel, it will first make sure the
map image is set, and then will call the draw() method to paint all
agents and wireless ranges.
This method is from being a ControllerListener, everytime the Controller
notifies us, we refresh the user information in the all fields, and check
for a new photo of the current location and heading.
This method is used to make the JPanel re draw itself, usually because
some information or location has caused an Agent to change or created
a new Agent in the Simulator.