title: Django is not invoking my app's ready method
body: <p>I have a Django project called <strong>expenses</strong>, and an app called <strong>expenseitems</strong>. In the project settings INSTALLED_APPS contains <code>expenses.expenseitems</code>. When I invoke the migrate command, the database is set up and the tables are created as expected.</p>
  
  <p>My end goal is to create a group-level permission for my model. So I want to invoke a method after migration is complete. However, while the ready methods in the AppConfigs for <code>django.contrib.auth</code> or <code>django.contrib.admin</code> are invoked when running <strong>migrate</strong>, the <em>ready</em> method for my app is not called. </p>
  
  <p>Here is my apps.py:</p>
  
  <pre><code>from django.apps import AppConfig
  from django.db.models.signals import post_migrate
  
  
  def initialization(sender, **kwargs):
      from django.contrib.auth.models import Group, Permission
      public, created = Group.objects.get_or_create(name="public")
      if not public.permissions.filter(codename="change_expenseitems").exists():
          perm = Permission.objects.get(codename="change_expenseitems")
          public.permissions.add(perm)
  
  
  class ExpenseitemConfig(AppConfig):
      name = 'expenses.expenseitems'
  
      def ready(self):
          post_migrate.connect(initialization, sender=self)
  </code></pre>
  
  <p>Any suggestions on what I'm missing?</p>