SP4: delete source of a linked page: please indicate the links in the warning (not only sub-pages) + remove linked copy statuts on delete

1) There is no warning when you delete the source of a linked copy. We should not indicate only sub-pages but also possible linked copies when deleting an object.

2) Ideally there should be an option to decide of the impact on linked destination copies. Either the editor could also mark them for deletetion or turn them into simple copies (no link any more). If we do not have the time to make something like that for SP4, please at lest turn them into classical copies (so that we could edit them if the source does not exist any more) and postpone afterwards for improvements for SP5.