Add django.contrib.messages to INSTALLED_APPS of example

Author: daniviga

example/testapp/settings.py

@@ -55,6 +55,7 @@
     'django.contrib.sessions',
     'django.contrib.admin',
     'django.contrib.staticfiles',
+    'django.contrib.messages',
     'adminsortable2',
     'testapp',
 ]