QT Apps not build on Linux/Mac?

Seems to me that we are not compiling the qt apps in OpenMesh anymore. Might be related to the docker changes.

We should build the qt apps again. As in OF, we need one config file/option to specify the version and map it to the location of the installed qt versions.

Currently we should test on linux against 5.15.1 and 6.0.0 /ACG/acgdev/gcc-x86_64/qt/6.0.0/gcc_64/ /ACG/acgdev/gcc-x86_64/qt-5.15.1/5.15.1/gcc_64/