Reworked sys_color_changed() functions

Fixed OSX specific bugs:
- toolbar flashing for some mainframe sizes (Retina specific)
- size of mainframe when settings layout in slNew mode

Added missed icons to the "white" folder

src/slic3r/GUI/OptionsGroup.hpp

@@ -280,6 +280,7 @@ public:
     void        Show(const bool show);
     bool        update_visibility(ConfigOptionMode mode);
     void        msw_rescale();
+    void        sys_color_changed();
 	boost::any	config_value(const std::string& opt_key, int opt_index, bool deserialize);
 	// return option value from config 
 	boost::any	get_config_value(const DynamicPrintConfig& config, const std::string& opt_key, int opt_index = -1);