Switch to webpack workflow

A set of changes to match Blip and Clamshell's front-end workflow with Webpack.

@cheddar Do you want to take a look and tell me what you think? Thanks!
Outside the scope of this PR :) This is a file that was renamed (from `main.js` to `app.js`). I don't even know if I'm the one that wrote this code.

Would you like me to change this in this PR?