Revamp the interface with a modern toolkit.

[jorgebotas]

We use very few external libraries for the frontend (and for the backend!):

• dat.gui
• sweetalert2

This makes the code quite simple, but the interface is way from pretty.

We could use something like https://github.com/vuetifyjs/vuetify (a vue ui library based on material design) to create a nicer user experience. Or anything like that.