Add ``published`` manager to the ``Application``.

This manager will improve the syntax to retrieve applications
that have been published.
Update ``search`` filter to use the published manager.

This syntax is more readable and explains the items
returned in the query at glance.
Add ``app`` manager mechanics to retrieve the latest featured application.

https://github.com/madewithbytes/us_ignite/issues/156

The ``get_featured`` method will return the latest featured ``app``,
if available.
Add ``hub`` manager mechanics to retrieve the latest featured hub.

https://github.com/madewithbytes/us_ignite/issues/156

The ``get_featured`` method will return the latest featured ``hub``,
if available.
Add ``resource`` manager mechanics to retrieve the latest featured resource.

https://github.com/madewithbytes/us_ignite/issues/156

The ``get_featured`` method will return the latest featured ``resource``,
if available.
Add dummy placeholder.
Add featured objects to the ``homepage``.

https://github.com/madewithbytes/us_ignite/issues/156

A ``section`` app has been added to manage any semi-static
sections of the application.

The homepage shows the latest featured item for the:
 - ``Application``
 - ``Hub``
 - ``Resource``
Add ``image`` field to the ``Resource``.