pbjs: write RPC method stream info to JSON output
pbjs: write RPC method stream info to JSON output

The pbjs tool currently does not export RPC method stream information to
the JSON format, however, the Builder expects it in the JSON input. This
is fixed by setting request_stream and response_stream in the JSON
output of pbjs.

Fixes #468

noveyak/protobuf.js,noveyak/protobuf.js