Implementing the prerequisites for background fetch

There are three steps involved in supporting background fetch in your app:

1. Add the background fetch capability to your app.
2. Ask iOS to wake your app up.
3. Implement application(_:performFetchWithCompletionHandler:) in AppDelegate.

You can implement step 1 and 2 right now; step 3 will be implemented separately because this step will involve writing the code to fetch and update the movies using a helper struct.