removed index.html to app/assets and set brunch to build on heroku

Many students are having merge conflicts with the files in the public folder.  This is because brunch builds them.  The app/assets directory gets built into the public folder.  Thus app/assets/index.html and any other html file under assets will get built to public.  This works in development and due to a change to the package.json file, it works on Heroku as well.

A pull request for the course material is coming to match these changes.