Deployment on Google App Engine Fix #86

Pull request for deployement on GAE (fix #86).
All comments have been taken into account except the one about BasicAuthenticator (cf below).

> xhanin commented on bc799fe 3 days ago
> I'm not sure that's very useful. If you need to authenticate only an admin like that, it can be done with a > BasicAuthenticator directly, no need to implement UserRepository

You could find a restx project setup for GAE here (see commits with prefix 'GAE:'): https://github.com/boillodmanuel/gae-restx-poc