CLIMATE-468 - Add helpful links to VM build desktop

- Add desktop shortcut to the checkout OCW code base.
- Add desktop shortcut for starting up the UI backend. Once this has
  been started you can use the UI by opening Firefox and pointing the
  browser to the URL displayed in the terminal.
- Set the default desktop environment to Unity. The shortcuts rely on
  being able to boot up a file browser. For simplicity Nautilus was
  chosen. XFCE is great for testing, but it's not the most user friendly
  and it's rather out of date looking. For the likely users of the VM it
  makes sense to have the default desktop environment be a bit nicer
  looking.