Draft: Support HTTP requests alongside ZMQ for the webservice

@schmidtp this is a rough draft of what we discussed, enabling HTTP requests to the webservice alongside ZMQ requests. I assume we'll switch myMdC over to using the HTTP API, and once we're happy with that we'll clean up the ZMQ code.

I haven't yet tested doing actual requests with this; dark requests in particular likely need a bit more work. But I can do check_connection over both ZMQ & HTTP, so the concept of serving both at once seems to be feasible.