Changed convention for modules storing AppConfigs.

If you're creating a pluggable app called "Rock ’n’ roll", here's how you

would provide a proper name for the admin::

    # rock_n_roll/app.py

    # rock_n_roll/apps.py

    from django.apps import AppConfig

        name = 'rock_n_roll'

        verbose_name = "Rock ’n’ roll"

You would then tell your users to add ``'rock_n_roll.app.RockNRollConfig'`` to

their :setting:`INSTALLED_APPS`.

You would then tell your users to add ``'rock_n_roll.apps.RockNRollConfig'``

to their :setting:`INSTALLED_APPS`.

The recommended convention is to put the configuration class in a submodule of

the application called ``app``. However, this isn't enforced by Django.

the application called ``apps``. However, this isn't enforced by Django.

You must include the :attr:`~django.apps.AppConfig.name` attribute for Django

to determine which application this configuration applies to. You can define