Erasure encoding availability (#345)

* Erasure encoding availability initial commit

 * Modifications to availability store to keep chunks as well as
   reconstructed blocks and extrinsics.
 * Gossip messages containig signed erasure chunks.
 * Requesting eraure chunks with polkadot-specific messages.
 * Validation of erasure chunk messages.

* Apply suggestions from code review

Co-Authored-By: Luke Schoen <ltfschoen@users.noreply.github.com>

* Fix build after a merge

* Gossip erasure chunk messages under their own topic

* erasure_chunks should use the appropriate topic

* Updates Cargo.lock

* Fixes after merge

* Removes a couple of leftover pieces of code

* Fixes simple stuff from review

* Updates erasure and storage for more flexible logic

* Changes validation and candidate receipt production.

* Adds add_erasure_chunks method

* Fixes most of the nits

* Better validate_collation and validate_receipt functions

* Fixes the tests

* Apply suggestions from code review

Co-Authored-By: Robert Habermeier <rphmeier@gmail.com>

* Removes unwrap() calls

* Removes ErasureChunks primitive

* Removes redundant fields from ErasureChunk struct

* AvailabilityStore should store CandidateReceipt

* Changes the way chunk messages are imported and validated.

 * Availability store now stores a validator_index and n_validators for
 each relay_parent.
 * Availability store now also stores candidate receipts.
 * Removes importing chunks in the table and moves it into network
 gossip validation.
 * Validation of erasure messages id done against receipts that are
 stored in the availability store.

* Correctly compute topics for erasure messages

* Removes an unused parameter

* Refactors availability db querying into a helper

* Adds the apis described in the writeup

* Adds a runtime api to extract erasure roots form raw extrinsics.

* Adds a barebone BlockImport impl for avalability store

* Adds the implementation of the availability worker

* Fix build after the merge with master.

* Make availability store API async

* Bring back the default wasmtime feature

* Lines width

* Bump runtime version

* Formatting and dead code elimination

* some style nits (#1)

* More nits and api cleanup

* Disable wasm CI for availability-store

* Another nit

* Formatting

polkadot/network/src/validation.rs

@@ -27,7 +27,7 @@ use polkadot_validation::{
 use polkadot_primitives::{Block, BlockId, Hash};
 use polkadot_primitives::parachain::{
 	Id as ParaId, Collation, OutgoingMessages, ParachainHost, CandidateReceipt, CollatorId,
-	ValidatorId, PoVBlock
+	ValidatorId, PoVBlock,
 };
 
 use futures::prelude::*;
@@ -243,7 +243,7 @@ impl<P, E, N, T> ParachainNetwork for ValidationNetwork<P, E, N, T> where
 				let table_router_clone = table_router.clone();
 				let work = table_router.checked_statements()
 					.for_each(move |msg| { table_router_clone.import_statement(msg); Ok(()) });
-				executor.spawn(work.select(exit).map(|_| ()).map_err(|_| ()));
+				executor.spawn(work.select(exit.clone()).map(|_| ()).map_err(|_| ()));
 
 				table_router
 			});