Update the xcodeproj project file

This update should fix reported issues about failing to create an
NSPersistentStoreCoordinator with a nil model.

Also, reenables the ability to edit the core data model. Before you
couldn't have done that, because the project file was invalid.

For those of you having the same issue, think if you ever renamed your
project using the refactor xcode feature, if you did, you should take a
look there first. XCode messes things up.