- check out https://realm.io/news/gwendolyn-weston-ios-background-networking/ part called 'Recreating Tasks in application:handleEventsForBackgroundURLSession:identifier'
- check out this https://www.objc.io/issues/5-ios7/multitasking/#nsurlsessiondownloadtask and compare with the above
- lifecycle of a background urlsessiontask https://developer.apple.com/library/ios/documentation/Cocoa/Conceptual/URLLoadingSystem/NSURLSessionConcepts/NSURLSessionConcepts.html#//apple_ref/doc/uid/10000165i-CH2-SW42
- test on real device: https://forums.developer.apple.com/message/42353#42353
- try testing with and without UIApplicationExitsOnSuspend = YES