Refactor consensus code into polkadot/substrate components

[rphmeier]

The BFT code just needs a couple of things:

• Messages in
• Messages out
• Sign message with local key
• Round proposer
• Round timeouts
• Proposal generation function
• Proposal evaluation function

The proposal generation and evaluation functions should encapsulate the behavior of the specific substrate chain. This can be packaged up into its own trait.

We can package this up in a substrate-bft crate.

polkadot-statement-table crate:
The details of the proposal generation/evaluation function are what encapsulates the current statement table logic. This needs

• Misbehavior type
• Import of incoming statements
• Incoming statements to trigger fetch of candidate data for evaluation of availability
• Signing statements
• Creation of batches of outgoing messages (to be done on a timer or by some other heuristic)

polkadot-consensus crate:

• service built on top of the substrate-network
• maintains connections to authorities
• combined router for substrate-bft and polkadot-statement-table messages
• manages local consensus identity and signing of messages
• collates local parachain candidate
• fetches and evaluates other candidates as necessary
• creates full substrate block from statement table and transaction queue
• accumulates misbehavior to be evaluated on-chain

[gavofyork]

is this done @rphmeier & @arkpar ?

[rphmeier]

yes, I would say so