backend: fixed recursion error on getFullItem: getFullItem was doing a deepcopy of the item which could lead to infinite recursion if element had children. This has been fixed by doing a specialised copy function. For the same reason, an itemDataCopy function has also been implemented.

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