title: Installation of django-scheduler: $python manage.py runserver returns KeyError: u'__module__'
body: <p>I installed django-scheduler with pip (<a href="https://github.com/llazzaro/django-scheduler" rel="nofollow">https://github.com/llazzaro/django-scheduler</a>) and I edited settings.py as in the tutorial. When I run $python manage.py runserver I got this:</p>
  
  <pre><code>python manage.py runserver
  Traceback (most recent call last):
    File "manage.py", line 10, in &lt;module&gt;
      execute_from_command_line(sys.argv)
    File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 385, in execute_from_command_line
      utility.execute()
    File "/usr/local/lib/python2.7/dist-packages/django/core/management/__init__.py", line 354, in execute
      django.setup()
    File "/usr/local/lib/python2.7/dist-packages/django/__init__.py", line 21, in setup
      apps.populate(settings.INSTALLED_APPS)
    File "/usr/local/lib/python2.7/dist-packages/django/apps/registry.py", line 108, in populate
      app_config.import_models(all_models)
    File "/usr/local/lib/python2.7/dist-packages/django/apps/config.py", line 202, in import_models
      self.models_module = import_module(models_module_name)
    File "/usr/lib/python2.7/importlib/__init__.py", line 37, in import_module
      __import__(name)
    File "/usr/local/lib/python2.7/dist-packages/django_scheduler-0.7.5-py2.7.egg/schedule/models/__init__.py", line 1, in &lt;module&gt;
      from schedule.models.calendars import *
    File "/usr/local/lib/python2.7/dist-packages/django_scheduler-0.7.5-py2.7.egg/schedule/models/calendars.py", line 110, in &lt;module&gt;
      class Calendar(with_metaclass(ModelBase, *get_model_bases())):
    File "/usr/lib/python2.7/dist-packages/six.py", line 617, in with_metaclass
      return meta("NewBase", bases, {})
    File "/usr/local/lib/python2.7/dist-packages/django/db/models/base.py", line 71, in __new__
      module = attrs.pop('__module__')
  KeyError: u'__module__'
  </code></pre>
  
  <p>I tried to reinstall Python (2.7), Django (1.7) and the app. I need a calendar app to my project and this seems the most complete. </p>
  
  <p>Thanks.</p>