Add a heuristic to determine if we can skip merging a `NSManagedObjectContextDidSaveNotification` to avoid merging changes that are already available. refs #1351
Merge remote-tracking branch 'origin/bugfix/1351-ghost-objects-in-merge-notifications' into feature/1232-improve-performance
Set a maximum operation count of 50 within the importer so that very large import operations do not die due to resource exhaustion
Apply a few small optimizations to the fetch request cache

* Optimize single identification attribute computation
* Replace `NSCache` with dispatch queue guarded dictionary