Add admin for ``Feature`` and ``Domain`` models.
Add management command to load ``Domain`` and ``Feature`` fixtures.

https://github.com/madewithbytes/us_ignite/issues/81

The management command will load the initial tags for
the ``Application`` app.
Add fabric command to load initial fixtures.

https://github.com/madewithbytes/us_ignite/issues/81

The command will confirm that the initial fixtures should
be loaded.