Short-circuit consensus

Large file values cause the consensus code to fail, due to overflowing udp packets. If a packet like this is encountered all write ops come to a halt and doozerd is not fully operational anymore. As we run doozerd in a single machine setup we're not dependent on the consensus code.

This change short-circuit that by passing the same channel as in and out channel to the proposer used a by the peer. Additionally we get rid of the marshaling of the packets into protobuf as it never goes on the wire.