Now by default Newsstand starts with a demo shelf containing our demo books, including a tutorial book.
Merge branch 'master' into paid-subscriptions
Support for unset PURCHASES_URL constant

When the PURCHASES_URL constant is not set, Baker will not try to hit the endpoint.
Alert message for unsuccessful subscription

The message will be shown when no SKProduct corresponding to the subscription can be found.
Only show Free Subscription when not subscribed

Even if PURCHASES_URL is not set, Baker can keep track of when a free subscription has been purchased and hide the corresponding button.
Added generic title for subscription action sheet

The title will be used when PURCHASES_URL has not been set (i.e. when Baker has no way of determining whether a user is currently subscribed or not).