Implementation for #6216

* Implementation for #6216 - Make number keys select extruder when object treeview has focus
+ deleted unused extruder_selection()
+ Fixed notification after splitting of the solid object

* Follow up https://github.com/prusa3d/PrusaSlicer/commit/85a10268b9eabfa8aac4c7b1361136b40b75f9f0 - OSX implementation
+ Added shortcuts description to the "Keyboard Shortcuts" dialog

* Workaround to use "+/-" and numbers shortcuts on Linux
+ Fixed build on Linux

* OSX specific: fixed a work of keyboard accelerators from numbers on NumPad keyboard

* KBShortcutsDialog: fixed shortcuts for "Preferences" and "Show/Hide 3Dconnexion devices settings dialog, if enabled" under osx
and "Set Printable/Unprintable" and "Set extruder" under Linux
 + OSX specific: Added minimize of the application on "Cmd+M"

* Hot-fix for https://github.com/prusa3d/PrusaSlicer/commit/6efeb9d6b433f49aaca8ee42ed02d824c452eb8e

* Removed Linux specific workaround

src/slic3r/GUI/GLCanvas3D.cpp

@@ -2205,9 +2205,19 @@ void GLCanvas3D::on_char(wxKeyEvent& evt)
 #ifdef _WIN32
             if (wxGetApp().app_config->get("use_legacy_3DConnexion") == "1") {
 #endif //_WIN32
+#ifdef __APPLE__
+            // On OSX use Cmd+Shift+M to "Show/Hide 3Dconnexion devices settings dialog"
+            if ((evt.GetModifiers() & shiftMask) != 0) {
+#endif // __APPLE__
                 Mouse3DController& controller = wxGetApp().plater()->get_mouse3d_controller();
                 controller.show_settings_dialog(!controller.is_settings_dialog_shown());
                 m_dirty = true;
+#ifdef __APPLE__
+            } 
+            else 
+            // and Cmd+M to minimize application
+                wxGetApp().mainframe->Iconize();
+#endif // __APPLE__
 #ifdef _WIN32
             }
 #endif //_WIN32