Spike for perceived performance on Admin screen

The important part to look at is the JaverScrips.

1. In `AdminRoute` I skipped over the `model` hook, this allows the template to render immediately.
2. The Model find is done in the `setupController` hook.
3. I created a property `isLoading` that can be used in the template.

The uglyish bit probably specific to the Admin screens:
The `AdminIndexRoute` inherits the data from `AdminRoute`. I'm guessing Ember pulls it from whatever the `model` hook returns. Since we don't implement the `model` hook, the `AdminIndexController` `model` property is empty. To fix this I created an alias `model: Em.computed.alias('controllers.admin.model')`