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/libslic3r/Fill/FillBase.hpp

@@ -11,13 +11,13 @@
 
 #include "../libslic3r.h"
 #include "../BoundingBox.hpp"
-#include "../PrintConfig.hpp"
 #include "../Utils.hpp"
 
 namespace Slic3r {
 
 class ExPolygon;
 class Surface;
+enum InfillPattern : int;
 
 class InfillFailedException : public std::runtime_error {
 public:

src/libslic3r/ModelArrange.cpp

@@ -1,4 +1,6 @@
 #include "ModelArrange.hpp"
+
+#include <libslic3r/Model.hpp>
 #include "MTUtils.hpp"
 
 namespace Slic3r {

src/libslic3r/ModelArrange.hpp

@@ -1,11 +1,14 @@
 #ifndef MODELARRANGE_HPP
 #define MODELARRANGE_HPP
 
-#include <libslic3r/Model.hpp>
 #include <libslic3r/Arrange.hpp>
 
 namespace Slic3r {
 
+class Model;
+class ModelInstance;
+using ModelInstancePtrs = std::vector<ModelInstance*>;
+
 using arrangement::ArrangePolygon;
 using arrangement::ArrangePolygons;
 using arrangement::ArrangeParams;

src/libslic3r/PrintConfig.hpp

@@ -33,7 +33,7 @@ enum PrintHostType {
     htOctoPrint, htDuet, htFlashAir, htAstroBox
 };
 
-enum InfillPattern {
+enum InfillPattern : int {
     ipRectilinear, ipMonotonous, ipGrid, ipTriangles, ipStars, ipCubic, ipLine, ipConcentric, ipHoneycomb, ip3DHoneycomb,
     ipGyroid, ipHilbertCurve, ipArchimedeanChords, ipOctagramSpiral, ipCount,
 };

src/libslic3r/Slicing.hpp

@@ -11,7 +11,6 @@
 
 #include "libslic3r.h"
 #include "Utils.hpp"
-#include "PrintConfig.hpp"
 
 namespace Slic3r
 {
@@ -19,6 +18,7 @@ namespace Slic3r
 class PrintConfig;
 class PrintObjectConfig;
 class ModelObject;
+class DynamicPrintConfig;
 
 // Parameters to guide object slicing and support generation.
 // The slicing parameters account for a raft and whether the 1st object layer is printed with a normal or a bridging flow