Include cleanup: Selection.hpp

It does not need 3DScene.hpp and Model.hpp
And it does not to be included by GLGizmoBase.hpp

src/slic3r/GUI/Gizmos/GLGizmoHollow.hpp

@@ -5,12 +5,17 @@
 #include "slic3r/GUI/GLSelectionRectangle.hpp"
 
 #include <libslic3r/SLA/Hollowing.hpp>
+#include <libslic3r/ObjectID.hpp>
 #include <wx/dialog.h>
 
 #include <cereal/types/vector.hpp>
 
 
 namespace Slic3r {
+
+class ConfigOption;
+class ConfigOptionDef;
+
 namespace GUI {
 
 enum class SLAGizmoEventType : unsigned char;