Rolling: #314 Implement app icon & name chooser (Icon chooser not yet completed)

Since there are some missing details about app icon standards, it is hard to implement icon chooser.  So I make a pull request anyway :)
You'll see that this has been updated in the latest codebase to:
`PUBLISH_ENDPOINT=https://webmaker-app-publisher.mofodev.net/publish/webmaker-app`