title: Django cannot makemigrations for a nested app
body: <p>I am trying to create a nested app in my django project, but <code>makemigrations</code> is not detecting it. I have the following directory structure:</p>
  
  <pre><code>myproject/
  ├── db.sqlite3
  ├── manage.py
  ├── myproject
  │   ├── __init__.py
  │   ├── settings.py
  │   ├── urls.py
  │   └── wsgi.py
  └── parentapp
      ├── admin.py
      ├── apps.py
      ├── childapp
      │   ├── admin.py
      │   ├── apps.py
      │   ├── __init__.py
      │   ├── migrations
      │   │   └── __init__.py
      │   ├── models.py
      │   ├── tests.py
      │   └── views.py
      ├── __init__.py
      ├── migrations
      │   └── __init__.py
      ├── models.py
      ├── tests.py
      └── views.py
  </code></pre>
  
  <p>And here is some relevant code:</p>
  
  <p><strong>myproject/myproject/settings.py:</strong></p>
  
  <pre><code>INSTALLED_APPS = [
      ...
      'parentapp',
      'parentapp.childapp',
  ]
  </code></pre>
  
  <p><strong>myproject/parentapp/childapp/__init__.py:</strong></p>
  
  <pre><code>default_app_config = "parentapp.childapp.apps.ChildAppConfig"
  </code></pre>
  
  <p><strong>myproject/parentapp/childapp/apps.py:</strong></p>
  
  <pre><code>from django.apps import AppConfig
  
  class ChildAppConfig(AppConfig):
      name = 'parentapp.childapp'
  </code></pre>
  
  <p><strong>myproject/parentapp/childapp/models.py:</strong></p>
  
  <pre><code>from django.db import models
  
  class Child(models.Model):
  
      class Meta:
          app_label = "parentapp.childapp"
  
      name = models.CharField(max_length=100)
  </code></pre>
  
  <p>I see the following behavior when trying to make migrations:</p>
  
  <pre><code>$ myproject/manage.py makemigrations
  No changes detected
  
  $ myproject/manage.py makemigrations childapp
  No changes detected in app 'childapp'
  
  $ myproject/manage.py makemigrations parentapp.childapp
  'parentapp.childapp' is not a valid app label.  Did you mean 'childapp'?
  </code></pre>
  
  <p>What am I doing wrong?  I see loads of other reusable apps that have nested apps (django-allauth, for example).  </p>