Implemented editing for extruder of existing ToolChangeCode tick

+ Code refactoring: DoubleSlider is extracted from wxExtensions

src/slic3r/GUI/Plater.cpp

@@ -84,6 +84,7 @@
 
 #include <wx/glcanvas.h>    // Needs to be last because reasons :-/
 #include "WipeTowerDialog.hpp"
+#include "libslic3r/CustomGCode.hpp"
 
 using boost::optional;
 namespace fs = boost::filesystem;