custom menu items

[vijithassar]

Allow the caller to add custom links to the menu.

To use this, add an array of items to the top level usermeta property of the specification, each of which is an object containing text and href properties.

specification.usermeta = {
  menu: {
    items: [
      { text: 'Example', href: 'https://www.example.com' }
    ]
  }
}