Behavior of the "cog" icon is changed to avoid misunderstandings appear in issue #4891:

"Cog" icon is enabled now every time, but it will had next behavior:
1. Add physical printer, if logical printer is selected
2. Edit physical printer, if it is selected.

 + PresetComboBox: Fixed the black rectangle instead of icon for the "Add/Remove presets" item

src/slic3r/GUI/PresetComboBoxes.hpp

@@ -59,6 +59,10 @@ public:
 
     void update(std::string select_preset);
 
+    void edit_physical_printer();
+    void add_physical_printer();
+    bool del_physical_printer(const wxString& note_string = wxEmptyString);
+
     virtual void update();
     virtual void msw_rescale();