CounterPanel Constructor
public CounterPanel(Counter ctr) {
incButton = new Button("+");
decButton = new Button("-");
valField = new TextField();
p.setLayout(new BorderLayout());
p.add(incButton, "North");
p.add(decButton, "South");
incButton.addActionListener(this);
decButton.addActionListener(this);
ctr.registerAsObserver(this);