Class documentation should not only say whether a class or function call is deprecated, but also mention the Qt version it got deprecated first.

We consider the latest documentation at http://doc.qt.io/qt-5/ to be valid for older versions. This is why we e.g. document the exact Qt version when a particular class or method got added (\since). Anyhow, we don't do so when deprecating things.

We could e.g. add a \deprecatedsince command, alongside \deprecated.