Change networking to not deserialize incoming messages early

[RitaMAllenCA]

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The networking component should become completely agnostic of the actual component payload and only announce incoming bytes, along with a channel tag. Actual reading should be left to the components themselves. Blocks: https://github.com/casper-network/casper-node/issues/3756 (this should replace the current block on that ticket) Blocks: "Factor out additional networking logic from networking component"

this ticket really should be split into two parts: One is prepping the networking component to be able to support sending "raw" data, and the other one is actually moving the network message deserialization from raw into components. For comparison, currently data is encoded/decoded in the networking interface instead of individual components, except for consensus, which has a weird double serialization going on.