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

substrate/polkadot/runtime/src/api.rs

@@ -14,7 +14,7 @@
 // You should have received a copy of the GNU General Public License
 // along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.
 
-use runtime::{system, parachains, consensus, session};
+use runtime::{system, parachains, consensus, session, timestamp};
 
 impl_stubs!(
 	execute_block => |block| system::internal::execute_block(block),
@@ -23,5 +23,6 @@ impl_stubs!(
 	validator_count => |()| session::validator_count(),
 	validators => |()| session::validators(),
 	authorities => |()| consensus::authorities(),
-	duty_roster => |()| parachains::calculate_duty_roster()
+	duty_roster => |()| parachains::calculate_duty_roster(),
+	get_timestamp => |()| timestamp::get()
 );