Share settings with app.

This allows Ember CLI to augment the settings if `broccoli-asset-rev` is
present (since in the addon world Ember CLI itself is not directly aware of
`broccoli-asset-rev`).

Specifically, we need to add `testem.js` to `excludes` if
`broccoli-asset-rev` is present. This will allow tests to run against
the production builds.
Merge pull request #9 from rjackson/share-preferences-with-app

Share settings with app.