Moved declaration of ´ fetchEntriesFromDataStore` to persistence manager
Some test refactoring to allow testing of multiple persistence manager implementations
Extracted common test code from CoreDataBasicTests
Extracted common test code from CoreDataQuerySyncTests
Added Realm as a dependency for the tests

This will be used to test a new persistence manager implementation using Realm.
Added timeout to async tests
Move use of NSManagedObject subclasses to CoreData specific tests
Skip `nil` in `mapFieldsToObject:usingMapping:`
Added an experimental persistence manager for Realm

Relationships are currently unsupported.
Resolve 1-to-1 relationships in `RealmManager`

one-to-many will need a more sophisticated way of determining which properties are relationships