Refactor background update

iOS13 has a new concept to do jobs in the background. We should move from BackgroundFetch to BackgroundTask. Our current implementation for background jobs can be find in AppDelegate.swift. See: https://developer.apple.com/documentation/backgroundtasks/bgtaskscheduler More examples: https://www.andyibanez.com/posts/modern-background-tasks-ios13/

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information