Added a project specific config to the PresetBundle class.

This project specific config will be stored into the config.ini,
into .3mf and .amf and .gcode,
and recover it from the same files.

xs/src/slic3r/GUI/PresetBundle.hpp

@@ -39,6 +39,11 @@ public:
     // extruders.size() should be the same as printers.get_edited_preset().config.nozzle_diameter.size()
     std::vector<std::string>    filament_presets;
 
+    // The project configuration values are kept separated from the print/filament/printer preset,
+    // they are being serialized / deserialized from / to the .amf, .3mf, .config, .gcode, 
+    // and they are being used by slicing core.
+    DynamicPrintConfig          project_config;
+
     bool                        has_defauls_only() const 
         { return prints.size() <= 1 && filaments.size() <= 1 && printers.size() <= 1; }