Add some methods around a fetch with localstorage as server

I'm playing around with using localstorage as a "server" and finding a
natural way to integrate that into this demo app. The idea of a 'fetch'
method is familiar from BackboneJS, so I'm starting there.

Still lots to do:
 * Pre-populate the localstorage "server" with dummy todo items in
'entry.js'
 * change the existing 'add' 'update' and 'delete' methods to persist
changes to the "server"
 * Call 'fetch' before rendering the 'todo_app' component
 * Compare this to the approach in the flux chat app example[1]

 [1]: https://github.com/facebook/flux/tree/master/examples/flux-chat