Use qtpaths.exe instead (or in addition to) qmake.exe to retrieve Qt version information

In some future Qt version, there might not be a qmake.exe anymore by default.
It's replacement is qtpaths.exe which behaves the same in regards the -query functionality.

Use qtpaths.exe already now to determine the properties of a Qt build.

Instead of selecting the .exe file the user might be allowed to just select a directory that contains qmake.exe / qtpaths.exe.