opam.ocaml.org integration

This should prepare ocaml.org to generate a template for opam.ocaml.org and host the necessary assets. No user-visible changes should occur after application.

Please review.
I absolutely agree but I was overridden for the short term to deliver features rather than decouple `opam2web`. There are at least 3 (more) packages that I want to pull out of `opam2web` and I think we could get quite a bit of benefit from reuse by ocaml.org.