Tests checking the feast ID mapping

[igneus]

For interop/feast_ids.csv there should be tests making sure that

• [ ] all calendarium-romanum celebration symbols still exist in the gem and feast titles match
• [ ] all CANTUS IDs mentioned in the table exist at CantusIndex (download the whole list of feast IDs from there, then check against it)
• [ ] all romcal feast IDs mentioned in the table exist in latest romcal release
• [ ] romcal/CANTUS feast names resemble (use some kind of fuzzy matching) the corresponding calendarium-romanum ones