affiliations XMPP handling: /!\ PostGreSQL minimal version raised to 9.5 (for upsert support) - affiliations can now be handler after node creation using XMPP: affiliationsGet, affiliationsSet (both for node owner) and affiliations (for an entity to know with which nodes it is affiliated on the service) are implemented - pgsql: getOrCreateEntities helping method has been implemented, it get entity_id and create missing entities when needed.

create table callbacks (
    service text not null,
    node text not null,
    uri text not null,
    PRIMARY KEY (service, node, uri)
);