Preserve order when removing duplicates for `format=short`

See #323. Deployed to staging, see:

http://staging.api.lobid.org/resource?name=Mein+Weg+%C3%BCber+die+Pyren%C3%A4en&format=short
http://staging.api.lobid.org/resource?name=Mein+Weg+%C3%BCber+die+Pyren%C3%A4en&format=ids
http://staging.api.lobid.org/resource?name=Mein+Weg+%C3%BCber+die+Pyren%C3%A4en&format=full

All have "Mein Weg über die Pyrenäen" as the top hit. Unlike the `short` format on production:

http://api.lobid.org/resource?name=Mein+Weg+%C3%BCber+die+Pyren%C3%A4en&format=short