Provide a prettier binary with baked-in Sagui configuration

[pirelenito]

Having a prettier as a CLI in the project node_modules would make sure that editors such as Atom, properly apply the desired formatting.

We should find a way to inform the user if their editor configuration and Sagui is different. Since they will be different processes, maybe we could write a tmp file that the Sagui development server process can pick up and inform the user.