avoid directly using Protobuf.Message

[tharvik]

Currently, many (72) classes extends Protobuf's Message instead of using as a data only structure. This leads to many weird work-arounds like having constructor taking an object as argument, having to redefine fields with Object.defineProperty, having to register each class, ... Having a more layered approch to outside communication would greatly help, separating network (WebSocket), encoding (protobuf) and actual use (the rest).