Proposal creation and evaluation to plug into BFT (#77)

* reshuffle consensus libraries

* polkadot-useful type definitions for statement table

* begin BftService

* primary selection logic

* bft service implementation without I/O

* extract out `BlockImport` trait

* allow bft primitives to compile on wasm

* Block builder (substrate)

* take polkadot-consensus down to the core.

* test for preemption

* fix test build

* Fix wasm build

* Bulid on any block

* Test for block builder.

* Block import tests for client.

* Tidy ups

* clean up block builder instantiation

* justification verification logic

* JustifiedHeader and import

* Propert block generation for tests

* network and tablerouter trait

* use statement import to drive creation of further statements

* Fixed rpc tests

* custom error type for consensus

* create proposer

* asynchronous proposal evaluation

* inherent transactions in polkadot runtime

* fix tests to match real polkadot block constraints

* implicitly generate inherent functions

* add inherent transaction functionality to block body

* block builder logic for polkadot

* some tests for the polkadot API

polkadot/collator/src/lib.rs

@@ -61,7 +61,7 @@ pub trait ParachainContext {
 	fn produce_candidate<I: IntoIterator<Item=(ParaId, Message)>>(
 		&self,
 		ingress: I,
-	) -> (parachain::BlockData, polkadot_primitives::Signature);
+	) -> (parachain::BlockData, polkadot_primitives::AccountId, polkadot_primitives::Signature);
 }
 
 /// Relay chain context needed to collate.
@@ -131,7 +131,7 @@ pub fn collate<'a, R, P>(local_id: ParaId, relay_context: R, para_context: P)
 		P: ParachainContext + 'a,
 {
 	Box::new(collate_ingress(relay_context).map(move |ingress| {
-		let (block_data, signature) = para_context.produce_candidate(
+		let (block_data, _, signature) = para_context.produce_candidate(
 			ingress.0.iter().flat_map(|&(id, ref msgs)| msgs.iter().cloned().map(move |msg| (id, msg)))
 		);