Add server status packet

[Ivorforce]

It would be good to have a status packet to query the server's current status (OK, uploads disabled, under maintenance, down, [...]).

It would look a bit like

GET /api/server/status

{
    "status": "ok"
}

The use-cases should be pretty obvious: Conveying this to any application for it to be able to do some interpretation based on it.

[jdiez17]

It's a good idea, but what if the backend server is down? Then that endpoint wouldn't even work. Maybe have https://status.mediacru.sh (hosted elsewhere), and return a similar response?

[Ivorforce]

Sure, that works.
I was simply thinking that if the server is down, I'll just get an error and handle that as a status ('Server Offline').