Stateful quick start

This pull request makes the quick-start demo stateful and recoverable...

- You can reload a demo in progress and it will redraw the grid, adjust the timer to account for actual elapsed time, adjust the counter and pick up where it left off. This makes it easy to recover if you have a fatal error mid-demo - you can simply refresh (or re-create) your browser window and pick up where you left off.

- Made the timer work for a stop/reset request, i.e. you can now tell how long it takes to delete a set of VMs.

- The state info is stored in the app engine datastore and is indexed by project. So my work in progress won't interfere with yours (I won't try to recover your tasks and vice versa) so long as we're using different projects.