Cluster HTTP server

[rexxars]

Currently, the node server is only running in a single process. We should probably fix this so it utilizes as many cores as available (or make it configurable). Not really sure whether we should use the node cluster module (Nuno told me not to :p) or set up individual tasks and load-balance them with Varnish or similar.

For this to work, we also need to revise the way modules are fetched from NPM (#1).