Redo protocol for proxy--broker messages

Switch to containing all communication between the proxy and the broker
in the HTTP response body. This will make things easier if we ever use
something other than HTTP communicate between different actors in the
snowflake system.

Other changes to the protocol are as follows:
- requests are accompanied by a version number so the broker can be
backwards compatable if desired in the future
- all responses are 200 OK unless the request was badly formatted

proxy/translation

@@ -1 +1 @@
-Subproject commit 120578ec9dbf0975fc9ac573130282f628b9747a
+Subproject commit bbf11bb0c9f1aca4f6b18c6505645f85e2fa1986