Slow launch and image loading (5.0-r1 GTK2/GTK3 on Win10)

@bachango you are using the latest official GTK3 release, not a dev build. You can get one from Download RawTherapee development builds
The latest version there at the time of writing is
RawTherapee_dev_5.0-r1-gtk3-51-gd2b4fe5e_WinVista_64.zip