Make group required decorator to return a ``TemplateResponse``.

This change eases the unit testing of the response.
Use a ``get_or_create`` strategy on users.

This is to avoid duplicated user creation.
Change ``ordering form`` markup as an include.

The ``ordering_form`` is not reusable accross templates,
provided that the markup is similar.
Add application listing view.

https://github.com/madewithbytes/us_ignite/issues/21

Anyone can see the applications that have been
submited and published.

The view is paginated and can be ordered by ``name``
of the ``Application``.

Closes #21.