privilege: improvment on last message sending on presence with `+notify`: - local entities subscribed to the presence of an other local entity which is connecting are now added to presence map. This helps getting their notification even if they didn't connect recently - nodes with `presence` access model are now also used for `+notify` - notifications are not sent anymore in case of status change if the resource was already present.

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