[Gui] So headers: remove unused includes

- also sort out some headers to be used in precompiled headers
- also move a boost header to precompiled headers

src/Gui/ExpressionCompleter.cpp

@@ -23,15 +23,14 @@
 #include "PreCompiled.h"
 
 #ifndef _PreComp_
-#include <QAbstractItemView>
-#include <QContextMenuEvent>
-#include <QLineEdit>
-#include <QMenu>
-#include <QTextBlock>
+# include <boost/algorithm/string/predicate.hpp>
+# include <QAbstractItemView>
+# include <QContextMenuEvent>
+# include <QLineEdit>
+# include <QMenu>
+# include <QTextBlock>
 #endif
 
-#include <boost/algorithm/string/predicate.hpp>
-
 #include <App/Application.h>
 #include <App/Document.h>
 #include <App/DocumentObject.h>