Add a dummy app

[courajs]

Takes most of the app code from #7, but puts it in the right place, and sets up configuration correctly. No acceptance tests yet, but I've made some progress.

[gr2m]

This is great, thanks @courajs! I wonder, can we still add an npm start script that starts the dummy app for manual debugging and fiddling around? That'd be great :) But that could be another issue and we can merge this in first.

[courajs]

ember start does start the dummy app :)

The app folder is what gets added to the app of any app consuming this addon. The dummy app is what gets served by ember serve inside an addon project, and what is available during acceptance tests. It consumes the addon itself by default, which is why it was showing up anyway when added to the app folder.

[gr2m]

thanks for the explanation, this is great 👍