Initial: Offchain Workers (#1942)

* Refactor state-machine stuff.

* Fix tests.

* WiP

* WiP2

* Service support for offchain workers.

* Service support for offchain workers.

* Testing offchain worker.

* Initial version working.

* Pass side effects in call.

* Pass OffchainExt in context.

* Submit extrinsics to the pool.

* Support inherents.

* Insert to inherents pool.

* Inserting to the pool asynchronously.

* Add test to offchain worker.

* Implement convenience syntax for modules.

* Dispatching offchain worker through executive.

* Fix offchain test.

* Remove offchain worker from timestamp.

* Update Cargo.lock.

* Address review comments.

* Use latest patch version for futures.

* Add CLI parameter for offchain worker.

* Fix compilation.

* Fix test.

* Fix extrinsics format for tests.

* Fix RPC test.

* Bump spec version.

* Fix executive.

* Fix support macro.

* Address grumbles.

* Bump runtime

substrate/core/state-machine/src/testing.rs

@@ -168,6 +168,10 @@ impl<H: Hasher> Externalities<H> for TestExternalities<H> where H::Out: Ord + He
 			&AnchorBlockId { hash: parent, number: parent_num },
 		).map(|(root, _)| root.clone())
 	}
+
+	fn submit_extrinsic(&mut self, _extrinsic: Vec<u8>) -> Result<(), ()> {
+		unimplemented!()
+	}
 }
 
 #[cfg(test)]