sped up Core Data and Realm by having larger transactions and removing logging

Hi Benoit, I took a quick look at your project and noticed that most of the benchmark time was taken just logging. So just by removing logging and making more changes per transaction (instead of a single transaction per insert), benchmark time went down to 1.5s for Core Data and 0.4s for Realm (on average).

BTW, I work on Realm, so if you have any questions about it, just ping me!