broaden_concept fails on items within collections

[maarten-vermeyen]

The current approach in broaden concept fails when encountering an item in a collection. This poses two problems:

1. the current function only follows the link to the fires broader concept
2. thesaurus.onroerenderfgoed.be runs on an older version of atramhasis. This means that the link to the collection is missing.

While we wait on an update release of thesaurus.onroerenderfgoed.be, a possible workaround for some use case might be found using an approach (to be implemented) using the narrower concepts instead.