Fixing build against wxWidgets 3.0

The wxString saga continues. wxWidgets 3.0 don't have the wxString::FromUTF8(const std::string&) overload, we must use the GUI::from_u8 helper
Also wxWidgets 3.0 don't allow to disable wxString->const char* conversion, so calling show_info(wxWindow*, wxString, const char*) was ambiguous
Several includes moved around

src/libslic3r/Extruder.cpp

@@ -1,4 +1,5 @@
 #include "Extruder.hpp"
+#include "PrintConfig.hpp"
 
 namespace Slic3r {