Implemented ObjectLayers class

+ some code refactoring

src/slic3r/GUI/GUI_ObjectLayers.hpp

@@ -0,0 +1,36 @@
+#ifndef slic3r_GUI_ObjectLayers_hpp_
+#define slic3r_GUI_ObjectLayers_hpp_
+
+#include "GUI_ObjectSettings.hpp"
+#include "wxExtensions.hpp"
+
+class wxBoxSizer;
+
+namespace Slic3r {
+class ModelObject;
+
+namespace GUI {
+class ConfigOptionsGroup;
+
+class ObjectLayers : public OG_Settings
+{
+    ScalableBitmap m_bmp_delete;
+    ScalableBitmap m_bmp_add;
+
+    int             field_width {8};
+
+public:
+    ObjectLayers(wxWindow* parent);
+    ~ObjectLayers() {}
+
+    void        update_layers_list();
+    void        add_layer() {};
+    void        del_layer() {};
+
+    void        UpdateAndShow(const bool show) override;
+    void        msw_rescale();
+};
+
+}}
+
+#endif // slic3r_GUI_ObjectLayers_hpp_