Fix the possibility to click on menu list item when they're hidden (IE8+)

On IE8+ (even 10) the menu list is active even when it's hidden.
If you click right under the menu bar you can access to its content.
It's usually not a problem with big screens resolutions but it may lead to wrong actions on Windows Phone.
I suggest to display:none the menu list items to avoid clicking on them when the menu is hidden.