Read price history

Forwards the query string to the Fly history service and returns that service's JSON. Scope markets:read. Served only while the venue-data switch is on; until then 403 venue_data_off and Fly is not called. The Fly server key stays on the server. Not cached. A 400 from the service is 400 invalid_request. A 403 that is not the server credential being refused is 403 invalid_request. A 404 is 404 market_not_found. A Fly 401 is 503 internal_error, because the caller's key was already accepted.