refactoring:

src/main/java/BattleShip/GridGUI.java

@@ -8,7 +8,7 @@ import java.awt.event.ActionListener;
 import java.util.ArrayList;
 import java.util.Random;
 
-public class GridGUI {
+public class GridGUI extends JPanel {
 
     ArrayList<BSButton> buttons = new ArrayList<BSButton>();
     ArrayList<Ship> allShips = new ArrayList<Ship>();