Bookmark compatibility layer: The new `bookmark_compat` module add a compatibility layer between XEP-0048 (with XEP-0049 private XML storage) and XEP-0402, i.e. it implements the `urn:xmpp:bookmarks:1#compat` feature.

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