Use $interval instead of pollingFactory

Replaces the pollingFactory with Angular's `$interval` service. Reduces LOC & it seems necessary as per the Protractor documentation:

```
Before performing any action, Protractor asks Angular to wait until the page is 
synchronized. This means that all timeouts and http requests are finished. If 
your application continuously polls $timeout or $http, it will never be registered 
as completely loaded. You should use the $interval service (interval.js) for 
anything that polls continuously (introduced in Angular 1.2rc3).
```

Source: https://github.com/angular/protractor/blob/master/docs/timeouts.md