Use protobuf to even further reduce message size when sending over message queue

[re7eal]

Currently, messages sending over message queue are in JSON string format which causes the payload to be printable string. Hence, the payload is encoded in base64 string which makes the size bigger than it should.

It is more suitable to send data in raw bytes rather than bytes of UTF-8 string by using protobuf.

[re7eal]

Merged to development branch. Commit afc4fbf.