feat(rxAppRoutes): Load nav menu from CDN

BREAKING CHANGES:
- `rxAppRoutes` is now a factory. `encoreRoutes` is now the Encore specific service/instance for the default navigation.
  - All references to `rxAppRoutes` should be updated to use `encoreRoutes`
- `createInstance` function removed from 'rxAppRoutes'.
- `rxAppRoutes` now promise based, allowing for delayed navigation loading.

Example usage:
```
appRoutes.getAll().then(function (routes) {
    scope.routes = routes;
});
```

Closes #470
Closes #522
Closes #520
Closes #557
Merge pull request #540 from rackerlabs/470-external-nav

470 External Nav