Simplify onionoo architecture

Currently onionoo is a service comprised of 4 VMs: two backends with the onionoo java apps serving and updating the data, and two frontends.

At the time the service was launched this architecture made a lot of sense, but I think now we could simplify its maintenance by reducing it to a backend with a web server (like nginx) with some aggressive caching.

I was hoping that we would get sooner to the point where onionoo would be retired, but given the current pace of development of the metrics pipeline, I personally think it makes sense to reduce this service now so that it is easier to maintain for metrics and tpa.

What do you think?