Use the User::createFromData() factory method instead of composing it

- Refactored the factory method to reside in DefaultEntity class, so that
  all entities extend from DefaultEntity can benefit from it.
- Use the factory method everywhere instead of composing the user object
  ourselves with $user = new User(); $user->initialize($data);


See also the discussion in https://github.com/sumocoders/Simple-Application-Framework/pull/42