Create HighScore.java

Messed up somewhere. Can you guys take a look?

Exception in thread "main" java.lang.ClassCastException: javax.swing.JPanel cannot be cast to javax.swing.JFrame
	at HighScore.addButton(HighScore.java:35)
	at HighScore.addComponentsToPane(HighScore.java:114)
	at HighScore.createGUI(HighScore.java:127)
	at HighScore.main(HighScore.java:132)