All following functions check if there is an overflow item/items in main menu.
checkMenuSize('pre') – prepends item/items to menu helper
checkMenuSize('app') – appends item/items to menu helper
shoptet.menu.splitMenu() – prepends item/items to menu helper
Please note, that items are checked right at the function call, if you adding menu item with eg. external font icon, you have to provide check after all content is loaded by yourself.