Gerbil ported to Qt5

After a long-standing bug with framebuffers in Qt5 is fixed since version 5.5.1, we recently finished our porting of Gerbil from Qt4 to Qt5.

This is very beneficial as Qt4 had its very own problems with framebuffer support. On some Windows systems, Gerbil would crash on startup not being able to create the framebuffers it needs to display spectral plots. This seems to be solved by the switch to Qt5, as well as problems with GL context switches reported on Linux systems. Finally, the switch to Qt5 makes building easier on Windows.

See our Github project page for the current sources using Qt5. If you for some reason need to work with Qt4, we are still maintaining the Qt4 version and back-porting features to it. Find it in the qt4 branch.