File dialog for any Linux desktop

[WickedSmoke]

Currently the project links with gtk-3 to bring in the file dialog used by src/engine/linux/os.cpp. Not only is this an older version of Gtk, but it does not support KDE users well. Please consider using the DBUS FileChooser instead. This is implemented by https://github.com/btzy/nativefiledialog-extended which can provide a static library (libnfd.a) when built like this:

cmake -DCMAKE_BUILD_TYPE=Release -DNFD_PORTAL=ON ..

This library could then be added to the lumixengine_linux_3rdparty_bin repository. I was able to compile LumixEngine this way as you can see in my repo.