[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/TaskElementColors.cpp

@@ -23,13 +23,11 @@
 #include "PreCompiled.h"
 
 #ifndef _PreComp_
+# include <boost/algorithm/string/predicate.hpp>
+# include <QColorDialog>
 # include <sstream>
 #endif
 
-#include <QColorDialog>
-
-#include <boost/algorithm/string/predicate.hpp>
-
 #include <App/ComplexGeoData.h>
 #include <App/Document.h>