added Level6 and Level7 class

GameProject/src/playground/Level6.java

@@ -0,0 +1,7 @@
+package playground;
+
+import SpacInvadersLevel;
+
+public class Level6 extends SpacInvadersLevel {
+
+}

GameProject/src/playground/Level7.java

@@ -0,0 +1,5 @@
+package playground;
+
+public class Level7 extends SpaceInvadersLevel {
+
+}