Tagged transaction queue integration (#893)

* Make the graph generic.

* Adapting pool API for the graph.

* Merge pool & graph.

* Restructure.

* Fix test of transaction pool.

* Get rid of node/transaction-pool.

* Compilation fixes.

* Test7

* Fix compilation of tests.

* Revert runtime changes.

* Add validate_transaction to test-runtime.

* Fix RPC tests.

* Add clearing of the old transactions.

* Trigger pool events.

* Use new queue API.

* Fix wasm build, re-export Hasher.

* No warning if validate transaction fails.

* Get rid of Into<u64> and use As

substrate/core/sr-primitives/src/traits.rs

@@ -78,7 +78,7 @@ pub trait BlockNumberToHash {
 	type BlockNumber: Zero;
 
 	/// The type of the hash.
-	type Hash;
+	type Hash: Encode;
 
 	/// Get the hash for a given block number, or `None` if unknown.
 	fn block_number_to_hash(&self, n: Self::BlockNumber) -> Option<Self::Hash>;