Gui: Optimize includes to reduce compile time

src/Gui/Selection.cpp

@@ -30,6 +30,7 @@
 #include <boost/algorithm/string/predicate.hpp>
 
 #include <App/Application.h>
+#include <App/Document.h>
 #include <App/DocumentObject.h>
 #include <App/DocumentObjectPy.h>
 #include <App/GeoFeature.h>
@@ -40,10 +41,12 @@
 #include <Base/UnitsApi.h>
 
 #include "Selection.h"
+#include "SelectionObject.h"
 #include "Application.h"
 #include "Document.h"
 #include "Macro.h"
 #include "MainWindow.h"
+#include "MDIView.h"
 #include "SelectionFilter.h"
 #include "Tree.h"
 #include "ViewProviderDocumentObject.h"