the man behind QtWebApp
Today I received an answer from Stefan, the man behind QtWebApp. He says his project is not being developed further, since it has reached its final destination in a commercial product. He will not add features or extend it, just provided bugfixes.
He is not interested in further development.
If you want to make web application, C++ probably isn't your best option. Scripting languages have web frameworks which are thoroughly developed and have "batteries" for almost every practical case.
You should take a look at the Cutelyst project.