Add new action to create a new instance of the viewer in macos

shortcuts_management/shortcuts_manager.cpp

@@ -74,6 +74,10 @@ void ShortcutsManager::initDefaultShorcuts()
     defaultShorcuts.insert(ZOOM_IN_MGLASS_ACTION_Y, Qt::Key_Asterisk);
     defaultShorcuts.insert(ZOOM_OUT_MGLASS_ACTION_Y, Qt::Key_Underscore);
 
+#ifdef Q_OS_MAC
+    defaultShorcuts.insert(NEW_INSTANCE_ACTION_Y, Qt::Key_N);
+#endif
+
 #endif
 }