Fixed Shutdown to truely shut down the sessionController actions and closes the thread.

Added testcode to RestartSessionControllerTest to test for no errors.

core/src/test/java/RestartSessionControllerTest.java

@@ -0,0 +1,30 @@
+import netwerkprog.game.server.controllers.SessionController;
+import org.junit.Test;
+
+public class RestartSessionControllerTest {
+
+    @Test
+    public void restartSessionController() {
+        SessionController sessionController;
+        Thread sessionThread;
+
+        sessionController = new SessionController();
+        sessionThread = new Thread(sessionController);
+
+        sessionThread.start();
+        try {
+            Thread.sleep(1000);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+        sessionController.shutdown();
+        try {
+            Thread.sleep(1000);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+        System.out.println(sessionThread.getState());
+        sessionThread = new Thread(sessionController);
+        sessionThread.start();
+    }
+}