I didn't realise that Cura already had a menu item. To prevent
Confusion, i've changed Cura.MenuItem to use UM.MenuItem and let all
other menus use Cura.MenuItem
It seems that the extra logic doesn't play well with a menu bar.
Since we don't need to make this menu invisible ever, there is no need for the
extra logic to hide it. As such we can just use the regular menu
CURA-8683