CORE-5386 Renamed apps.wikiurl to wiki_url.
CORE-6100 CORE-5386 Added ratings conversion.
CORE-5832 Minor refactor.
CORE-5832 Fix for clj-http error responses in common trap handler.

Refactored donkey.util/clj-http-error? function into clojure-commons.error-codes for use in the common trap function.
Adding this extra catch-clause to the trap function prevents it from attempting to JSON encode clj-http response maps with InputStream :body values.
Removed obsolete donkey.util.service/empty-response function (it's the same as calling (success-response)).