Add a Dart for AppEngine hello world sample application to StageHand.

I have created a small Hello World sample app for Dart on AppEngine in StageHand.

Is it possible to get this into the main repo?

Cheers,
/gustav
You could chain the futures here to avoid two levels of indent:
```
.then((_) => memcache.set(DEFAULT_KEY, 'there!'))
.then((_) => cacheInitialized = true);
```