Add methods to help decide if a insert/update/delete request should be performed in a managed object

Prevents duplicated objects in the data base. Duplicated records are created when the context is saved after a fetch request if the HTTP client implements `requestForInsertedObject`. These objects are created with a random UUID if there is no request for the inserted object.

In our case, we implemented `requestForInsertedObject` to create some objects remotely but the not the objects created after the search request, since they already exist both remotely and locally.

To replicate, simply implement the `requestForInsertedObject` method in the AppDotNetAPIClient.m returning nil (as if we would want to create a new user but not saving fetched posts) and save the context after `AFIncrementalStore` posts the `AFIncrementalStoreContextDidFetchRemoteValues` notification.

These simple methods will allow more granularity when deciding if the request has to be made and the default value will allow backwards compatibility.