Automatically enable and disable widget's CloudKit sync based on sync notifications

[skjiisa]

I'm definitely going to need to experiment with this, but I believe NSPersistentStoreRemoteChange will be fired whenever Core Data receives changes from CloudKit, including when it does a fresh sync on app launch. Right now, the widget always tries to manually pull from CloudKit to display the most up-to-date info possible, and only falls back to the local disk if the connection fails. I don't have data on this, but I would assume most users do not use Tickmate on multiple devices, and thus that sync every time the widget reloads is unnecessary. So what could be done instead, is have a property in the shared User Defaults that marks the last time a remote change was synced, and if one has never happened, or happened long enough ago, the widget doesn't bother with the CloudKit sync and just loads the data locally.