Serialize subtopic ids.
Serialize subtopic ids.

(This is not actually used, but it would be surprising if these were
the only ids in DossierJS that didn't support custom serialization.)

miguel-guedes/dossier.js,dossier/dossier.js,miguel-guedes/dossier.js,miguel-guedes/dossier.js,dossier/dossier.js,dossier/dossier.js