Collect requirements for a Catalogue front-end

[SchulzeStTSI]

Migrated from GitLab Issue #207

To create a better UI frontend for the Catalogue, complementing

• the limited available frontends (/query, /verify, and the user management) and
• the limited support for Catalogue-related functionality that's given by the XFSC Portal

… we need to gather requirements that a Catalogue frontend should have. Let's have an initial discussion here.