Summary: Qt6 library to start applications only once per user

Description:
For some applications it is useful or even critical that they are started
only once by any user. Future attempts to start the application should
activate any already running instance, and possibly perform requested
actions, e.g. loading a file, in that instance.

For console (non-GUI) applications, the QtSingleCoreApplication variant
is provided, which avoids dependency on QtGui.

This is a special build against Qt6.

Maintainer: nobody