Set host/namespace defaults to use ember-cli express server

With the the express server [being exposed](https://github.com/stefanpenner/ember-cli/pull/683) to custom user routes, this is a more viable option for out of the box development rather than relying on a running Django instance.

By default, the custom routes are name-spaced with "api", so we'll make this the default configuration in ember-django-adapter.