show progress on the actual create call, eliminate no-op state polling

The current behaviour of `heroku create` is to create the app with the API, then dump out all of the command line messaging afterwards, including the `Creating app-name...` bit. This has the effect of making the command look unresponsive for a few seconds will the API call is underway.

An alternate approach, which this branch implements, would be to print the `Creating app-name...` bit first, then create the app with the API, then finish the messaging when the create returns successfully.

The downside of this approach is not having the name of the new app when creating apps with random names. You can see the effect of this on the UX in the changed examples in the diff.

Also, I think we can at this point eliminate the create status polling. @pedro are you able to confirm that apps will always come back completed now?