Includes cleanup:

GUI_App.hpp      (should not include) MainFrame.hpp
MainFrame.hpp    Plater.hpp
ModelArrange.hpp Model.hpp
Slicing.hpp      PrintConfig.hpp
FillBase.hpp     PrintConfig.hpp
GUI_App.hpp      PrintConfig.hpp
OptionsGroup.hpp GUI_App.hpp

src/slic3r/GUI/DoubleSlider.cpp

@@ -2,6 +2,7 @@
 #include "libslic3r/GCode/PreviewData.hpp"
 #include "GUI.hpp"
 #include "GUI_App.hpp"
+#include "Plater.hpp"
 #include "I18N.hpp"
 #include "ExtruderSequenceDialog.hpp"
 #include "libslic3r/Print.hpp"