Fixes issue causing rows not to be filtered out by fetch predicate

- For some reason, since switching from nested contexts to merging changes during the NSMangedObjectContextDidSave notification, NSArrayController doesn't remove objects marked for deletion even though it should based on its fetch predicate.
- ArrangeObjects is called right after the fetch is performed which gives us a change to post-filter the results. Combining the fetchPredicate & filterPredicate (if any) and filtering the results resolves the issue.