Created attachment 136968 [details] [review]
TrollTech is long gone, while Qt itself is relatively future-proof (so far).
(We have a few more file types to register, so if everyone is OK with this, I'd like to start adding more registrations in the vnd.qt namespace.)
Bug about the other file types: https://bugreports.qt.io/browse/QTBUG-64435
Pushed in 363e903