Replace checks for `entityName` on NSManagedObject subclasses with `nameOfEntity`

`entityName` is declared on NSObject and was causing validation warnings when submitting to the App Stores.
Reverting back to `MR_entityName` and `entityName` until there's a clear answer to this issue

See http://rentzsch.tumblr.com/post/82453434093/apple-claims-mogenerators-methods for more information
Remove unused test fixture