Added batch updating to AERecord
Batch updates are using NSBatchUpdateRequest (new in iOS 8)
New class methods in NSManagedObject extension: batchUpdate, objectsCountForBatchUpdate, batchUpdateAndRefreshObjects, refreshObjects
Implemented batch updating in example project's "Update All" action
Fixed bug in example project (there was a crash on the first launch because there were no selected events)
Update README.md