Literature updating: duplicate doi in file to be manually checked

[keelinm]

It can happen that there are two rows with the same ss_doi in the excel file that we manually check. These would have different ss_ids. In the current flow we would assign action "add new item" to both (unless we notice the matching doi and do something about it manually!!). Then the first one will be added, and the second one will fail to be added because the doi already exists in the bibfile. This is not catastrophic because the second item will reappear the next time literature is searched and we will assign it action "add ss_id" .... but still it could be handled more neatly in the first place.