Merge pull request #569 from magicalpanda/feature/remove-mogenerator-boilerplate-methods

Don't use mogenerator methods in place of standard Core Data calls. Fixes #74, #568 and #571.
Fix missing entity names. This re-introduces a dependency on mogenerator (or at least the implementation of -entityName method), but shouldn't throw warnings when submitting to the iOS App Store
Rename the MR_entityName private method so that it doesn't conflict with the mogenerator-created entityName, which is common on managed object subclasses. Fixes #575.
Create NSPersistentStoreCoordinator factory method that can accept a model as an argument.
Add helper to create an in memory persistent store coordinator with a specific managed object model.
Added unit tests for NSPersistentStoreCoordinator factory functions.