Mark a date of synchronization in each entity of core data to solve the issue of multi-sync of the same content in parallel and deleting the old entities.

- Movie and Genre now have a property 'syncDate' in model's file.
- The sync's date is create just before the sync begins in MovieFeedService.
- Each method of sync and import new have a new parameter of sync's date.
- Update an entity if it's sync's date is older than the global sync's date.