Spike for a new API for declaring endpoints

We talked quite a bit about `init_app` as a general way to export modules of Superdesk, and make them pluggable in generic Eve apps. This is [already used in Citizendesk](https://github.com/sourcefabric-innovation/citizendesk-interface/blob/superdesk/citizendesk_interface/__init__.py#L19) and it is working good. Me and Petr try to stay as long as possible on the public and private Superdesk chats in order to discuss similar topics, in order to avoid misunderstandings and avoid wasting time