Update hello blockstack tutorial

[larrysalibra]

The hello blockstack app no longer reflects how our API works, it needs to be updated

https://github.com/blockstack/blockstack/blob/master/tutorials/hello-blockstack.md

[larrysalibra]

I've updated code in the text tutorial to match the current app generator / hello blockstack.

Code used in the video of the video tutorial needs to be updated to match.

@pstan26 Who's best positioned to do this? I think you and @shea256 made this originally.

[ghost]

What is the status here?

(naturally, video-tutorials have lot of update-effort. Possibly avoid them when under heavy dev)