2024.04.15

I made a submenu.
left to do:
1. separator for menu
2. checkbox menuItem
3. radiobox menuItem
4. adding processing events to menu items.
5. attaching a submenu: calculation above/below
6. fix the transition icon to the submenu. should always be on the right
7. When focus is lost or a click is not on the menu, the menu should close.
8. hide submenus when switch main MenuBar Items.