title: Core Data import at first app launch
body: <p>I have a problem with my data import at my app launch.
  At first launch, I create a lot of core data objects (almost 400 objects).
  The problem is, when I try the app in simulator, all seems to be right but on a device, I have to wait a lot of time because of my importation and maybe, the app crash (not everytime).</p>
  
  <p>Is someone ever had this problem ?
  Should I try to make my importation script more efficient ?
  Is some good practices about data importation with Core Data exists ?</p>
  
  <p>Thanks a lot in advance !</p>