Code refactoring:

- PresetCombpBoxes are extracted to the separate file.
- All preset icons are moved to the PresetComboBox from Preset and PresetBundle
- First "steps" to add physical printers to the printers list on the sidebar.

src/slic3r/GUI/GUI_ObjectList.cpp

@@ -88,9 +88,6 @@ ObjectList::ObjectList(wxWindow* parent) :
 {
     // Fill CATEGORY_ICON
     {
-        // Note: `this` isn't passed to create_scaled_bitmap() here because of bugs in the widget,
-        // see note in PresetBundle::load_compatible_bitmaps()
-
         // ptFFF
         CATEGORY_ICON[L("Layers and Perimeters")]    = create_scaled_bitmap("layers");
         CATEGORY_ICON[L("Infill")]                   = create_scaled_bitmap("infill");