title: ImportError: No module named apps error in Django Oscar - while including an app in INSTALLED_APPS
body: <p>I received this error when I tried to customize Oscar and add a app called promotions under INSTALLED_APPS</p>
  
  <pre><code>(oscar)Macs-MacBook-Air:cyshop Mac$ python manage.py migrate
  Traceback (most recent call last):
    File "manage.py", line 10, in &lt;module&gt;
      execute_from_command_line(sys.argv)
    File "/Users/Mac/virtualenvs/oscar/lib/python2.7/site-packages/django/core/management/__init__.py", line 338, in execute_from_command_line
      utility.execute()
    File "/Users/Mac/virtualenvs/oscar/lib/python2.7/site-packages/django/core/management/__init__.py", line 312, in execute
  django.setup()
    File "/Users/Mac/virtualenvs/oscar/lib/python2.7/site-packages/django/__init__.py", line 18, in setup
      apps.populate(settings.INSTALLED_APPS)
    File "/Users/Mac/virtualenvs/oscar/lib/python2.7/site-packages/django/apps/registry.py", line 85, in populate
      app_config = AppConfig.create(entry)
    File "/Users/Mac/virtualenvs/oscar/lib/python2.7/site-packages/django/apps/config.py", line 112, in create
      mod = import_module(mod_path)
    File   "/usr/local/Cellar/python/2.7.10_2/Frameworks/Python.framework/Versions/2.7/lib/python2.7/importlib/__init__.py", line 37, in import_module
      __import__(name)
  ImportError: No module named apps
  </code></pre>
  
  <p>I am not sure if it is not able to pick the apps folder under which I have added promotions. </p>
  
  <p>settings.py looks like this :</p>
  
  <pre><code>INSTALLED_APPS = [
      'django.contrib.admin',
      'django.contrib.auth',
      'django.contrib.contenttypes',
      'django.contrib.sessions',
      'django.contrib.messages',
      'django.contrib.staticfiles',
      'django.contrib.sites',
      'django.contrib.flatpages',
      'compressor',
      'widget_tweaks'
  ]
  
  from oscar import get_core_apps
  
  INSTALLED_APPS = INSTALLED_APPS + get_core_apps(
  ['apps.promotions'])
  </code></pre>
  
  <p>My file structure is: 
  |cyshop</p>
  
  <pre><code>|_init_.py
  
  |db.sqlite3
  
  |manage.py
  
  |settings.py
  
  |apps 
  
       |_init_.py
  
       |promotions
  
            |_init_.py
  
            |models.py
  
  |urls.py
  
  |wsgi.py
  </code></pre>
  
  <p>Please do help me out. Not sure why the ImportError takes place when I add an attribute into get_core_apps()</p>