Removed some obsolete Perl bindings.

Removed libslic3r from the default include paths for all modules but
libslic3r. Now headers from libslic3r need to be included with an
explicit path (libslic3r/libslic3r.h etc)
Split the localization macros into I18N.{cpp,h}

src/slic3r/GUI/GUI_Preview.cpp

@@ -3,6 +3,7 @@
 #include "GUI_Preview.hpp"
 #include "GUI_App.hpp"
 #include "GUI.hpp"
+#include "I18N.hpp"
 #include "AppConfig.hpp"
 #include "3DScene.hpp"
 #include "BackgroundSlicingProcess.hpp"
@@ -20,7 +21,7 @@
 #include <wx/checkbox.h>
 
 // this include must follow the wxWidgets ones or it won't compile on Windows -> see http://trac.wxwidgets.org/ticket/2421
-#include "../../libslic3r/Print.hpp"
+#include "libslic3r/Print.hpp"
 
 namespace Slic3r {
 namespace GUI {