add swip-27: strictly typed wire-level messages

[mfw78]

This PR revises the wire-level protocol communication used within Swarm so as to be comprehensively type-safe, building upon SWIP-26. It critically:

1. Unifies types across the protobufs used within Swarm.
2. Makes use of chunk types and versions so as to move heavy marshalling work from the implementations to protobuf libraries, reducing client code and therefore minimising potential errors.
3. Enforces a framework of stateless vs stateful protocols, providing a methodology by which to class protocols and ensure strongly typed messaging, eliminating any need for inference within the protocol.

The above reduces buffer overflow attacks, creates deterministic memory footprints, simplifies client development and much more ❤️