Dictionary returned by read queries should return null values too
Dictionary returned by read queries should return null values too

More details: https://github.com/Azure/azure-mobile-services/issues/699
Using NSDictionaryResultType causes the returned dictionary to not have
keys for properties with null values. This commit changes the fetch
result type to the default, and extracts a dictionary from the returned
managed object.

Azure/azure-mobile-apps-ios-client,Azure/azure-mobile-apps-ios-client,Azure/azure-mobile-apps-ios-client,Azure/azure-mobile-apps-ios-client