Verify header justification during import (#76)

* 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

* Fixed rpc tests

substrate/polkadot/primitives/src/block.rs

@@ -23,6 +23,8 @@ use rstd::vec::Vec;
 use codec::{Input, Slicable};
 use transaction::UncheckedTransaction;
 
+pub use primitives::block::Id;
+
 /// Used to refer to a block number.
 pub type Number = u64;