title: LookupError: No installed app with label 'app' (Django 1.11 / Python 2.7 / xadmin)
body: <p>Can't for the life of me figure out what the issue is. Help please!</p>
  
  <p>I'm trying to extend the admin view (using the xadmin app), by including a chart</p>
  
  <p>The issue started appearing with the addition of:</p>
  
  <p><strong>admin</strong></p>
  
  <pre><code>from xadmin import views    
  from .models import DGISummary
  ...
  
  @xadmin.sites.register(views.website.IndexView)
  class MainDashboard(object):
  widgets = [
      [
          {
              "type": "chart", 
              "model": "dgisummary",
              "chart": "reg_members",
              "params": 
              {
                  "_p_date__gte": "2017-01-01", 
                  "p": 1,
                  "_p_date__lt": "2017-12-01"
              }
          },
      ],
  ]
  </code></pre>
  
  <p><strong>model</strong></p>
  
  <pre><code>@python_2_unicode_compatible
  class DGISummary(models.Model):
      quarter = models.CharField(max_length=2,)
      reg_members = models.IntegerField()
      sub_received = models.IntegerField()
      ...
  
      class Meta:
          verbose_name = u"Summary"
          verbose_name_plural = verbose_name
  
      def __str__(self):
          return self.quarter
  </code></pre>
  
  <p>And the <strong>traceback</strong></p>
  
  <pre><code>System check identified no issues (0 silenced).
  February 20, 2018 - 15:38:35
  Django version 1.11.10, using settings 'csa_portal.settings'
  Starting development server at http://127.0.0.1:8000/
  Quit the server with CTRL-BREAK.
  ERROR:root:No installed app with label 'app'.
  Traceback (most recent call last):
    File "C:/../apps\xadmin\views\dashboard.py", line 563, in get_widgets
      ws.append(self.get_widget(widget))
    File "C:/../apps\xadmin\views\base.py", line 78, in method
      return filter_chain(filters, len(filters) - 1, _inner_method, *args, **kwargs)
    File "C:/../apps\xadmin\views\base.py", line 47, in filter_chain
      return func()
    File "C:/../apps\xadmin\views\base.py", line 72, in _inner_method
      return func(self, *args, **kwargs)
    File "C:/../apps\xadmin\views\dashboard.py", line 517, in get_widget
      wid_instance = widget_with_perm(self, data or widget.get_value())
    File "C:/../apps\xadmin\views\dashboard.py", line 325, in __init__
      super(ModelBaseWidget, self).__init__(dashboard, data)
    File "C:/../apps\xadmin\views\dashboard.py", line 200, in __init__
      if not self.is_valid():
    File "C:\Python27\lib\site-packages\django\forms\forms.py", line 183, in is_valid
      return self.is_bound and not self.errors
    File "C:\Python27\lib\site-packages\django\forms\forms.py", line 175, in errors
      self.full_clean()
    File "C:\Python27\lib\site-packages\django\forms\forms.py", line 384, in full_clean
      self._clean_fields()
    File "C:\Python27\lib\site-packages\django\forms\forms.py", line 402, in _clean_fields
      value = field.clean(value)
    File "C:\Python27\lib\site-packages\django\forms\fields.py", line 160, in clean
      value = self.to_python(value)
    File "C:/../apps\xadmin\views\dashboard.py", line 301, in to_python
      return apps.get_model(app_label, model_name)
    File "C:\Python27\lib\site-packages\django\apps\registry.py", line 200, in get_model
      app_config = self.get_app_config(app_label)
    File "C:\Python27\lib\site-packages\django\apps\registry.py", line 156, in get_app_config
      raise LookupError(message)
  LookupError: No installed app with label 'app'.
  </code></pre>
  
  <p>The strange thing is that there is a demo of the app, and I am basing my code off that. This includes the line:</p>
  
  <pre><code>class MainDashboard(object):
      widgets = [
          [
              {
              "type": "html", 
              "title": "Test Widget",
              "content": "&lt;h3&gt; Welcome to Xadmin! &lt;/h3&gt;&lt;p&gt;Join Online Group: &lt;br/&gt;QQ Qun : 282936295&lt;/p&gt;"
              },
              {
                  "type": "chart", 
                  "model": "app.accessrecord", 
                  "chart": "user_count",
                   "params": 
                      {
                      "_p_date__gte": "2013-01-08", 
                      "p": 1, 
                      "_p_date__lt": "2013-01-29"
                      }
               },
  </code></pre>
  
  <p>Not sure what's going on here. Any pointers would be appreciated.</p>
  
  <p><strong>EDIT</strong></p>
  
  <p>As requested, installed apps:</p>
  
  <pre><code>INSTALLED_APPS = [
      'admin_bootstrap',
      'survey',
      'xadmin',
      'django.contrib.admin',
      'django.contrib.auth',
      'django.contrib.contenttypes',
      'django.contrib.sessions',
      'django.contrib.messages',
      'django.contrib.staticfiles',
      'dashing',
      'formtools',
      'crispy_forms',
      'reversion',
  ]
  </code></pre>