Fix swift entity names

Currently it is necessary to set the class name of an entity in your data model to the fully qualified Swift classname, plus its parent module, i.e. "MyThingKit.Account". This PR updates mogenerator to any modules from the front of the class name returned from `- [NSEntityDescription managedObjectClassName]` so that it just becomes "Account" in generated Swift output.

There might be a nicer way to come at this, and using `pathExtension` to achieve the module stripping isn't semantically great — but it works OK. 

I'm happy to update this PR based on any feedback.