Moved apps back in the toplevel django namespace.

Reverted 4a56a93cc4.

django/contrib/admindocs/views.py

@@ -5,10 +5,10 @@ import re
 import warnings
 
 from django import template
+from django.apps import app_cache
 from django.conf import settings
 from django.contrib import admin
 from django.contrib.admin.views.decorators import staff_member_required
-from django.core.apps import app_cache
 from django.db import models
 from django.core.exceptions import ViewDoesNotExist
 from django.http import Http404