ITMS-90683 - App uses API/is entitled to use Photo Library

[dylmye]

The app doesn't currently read/write to the photo library, however we're getting the following message on iOS App Store submission:

ITMS-90683: Missing purpose string in Info.plist - Your app’s code references one or more APIs that access sensitive user data, or the app has one or more entitlements that permit such access. The Info.plist file for the “SetlistSherlock.app” bundle should contain a NSPhotoLibraryUsageDescription key with a user-facing purpose string explaining clearly and completely why your app needs the data. If you’re using external libraries or SDKs, they may reference APIs that require a purpose string. While your app might not use these APIs, a purpose string is still required. For details, visit: https://developer.apple.com/documentation/uikit/protecting_the_user_s_privacy/requesting_access_to_protected_resources.