bug fix: MenuItem and SubMenuItem could not be created with isPublic === false

Whenever the user created a new MenuItem or SubMenuItem with isPublic === false, isPublic was defaulted to the same value of the parent menu due to a bug in the comparison.
Maybe this should be defaulted to the parent menu items isPublic property rather than the parent menu isPublic. Something like this:
isPublic: isPublic === null && this.menus[menuId].items[itemIndex].isPublic || isPublic,