Update helloworld app to new dataflow

This is an in-progress PR. This works just like the old helloworld but also has a working data-ui and recordable rendering. @rkneufeld - we are looking to update the helloworld-app to use the new dataflow, in the same spirit as #31, right?

If so, what's mostly left to do is busy-work - adding copyright and rename helloworld-app2 to helloworld-app. I generated helloworld-app2 since it was easier to generate a new app than hack around the outdated sample app. I'll finish this up once I get confirmation this is a sample we want to update.