[meta] Refactor and make it a client side app

[bfabio]

The app is now a server side node application, but we can refactor it into a static client side app, plus a couple of support FaaS API endpoints

• Pick a client side framework (Pick a new client side framework #205)
• Implement the API call that generates the token and sends the confirmation email (Implement the API call that generates the token and sends the confirmation email #206)
• Implement the API call that validates the token (Implement the API call that validates the token #207)
• Use developers-italia-api with no local state (Use developers-italia-api for saving new publishers #203)