Define all items in global data file

[silveltman]

Define all items in global data file. Like so:

_data/navigation.yaml

items:
  - key: home
    title: Home
    url: /
    children:
      - key: Second
        title: Second
        url: /
        children:
  - key: contact
    title: Contact
    url: /contact

[terox]

This could be very useful for pages that use i18n