New sessions, kill consensus module (#2802)

* Draft of new sessions

* Reintroduce tuple impls

* Move staking module to new session API

* More work on staking and grandpa.

* Use iterator to avoid cloning and tuple macro

* Make runtime build again

* Polish the OpaqueKeys devex

* Move consensus logic into system & aura.

* Fix up system module

* Get build mostly going. Stuck at service.rs

* Building again

* Update srml/staking/src/lib.rs

Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>

* Refactoring out Consensus module, AuthorityIdOf, &c.

* Refactored out DigestItem::AuthoritiesChanged. Building.

* Remove tentative code

* Remove invalid comment

* Make Seal opaque and introduce nice methods for handling opaque items.

* Start to use proper digest for Aura authorities tracking.

* Fix up grandpa, remove system::Raw/Log

* Refactor Grandpa to use new logging infrastructure.

Also make authorityid/sessionkey static. Switch over to storing
authorities in a straight Vec.

* Building again

* Tidy up some AuthorityIds

* Expunge most of the rest of the AuthorityKey confusion.

Also, de-generify Babe and re-generify Aura.

* Remove cruft

* Untangle last of the `AuthorityId`s.

* Sort out finality_tracker

* Refactor median getting

* Apply suggestions from code review

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

* Session tests works

* Update core/sr-primitives/src/generic/digest.rs

Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>

* Session tests works

* Fix for staking from @dvc94ch

* log an error

* fix test runtime build

* Some test fixes

* Staking mock update to new session api.

* Fix build.

* Move OpaqueKeys to primitives.

* Use on_initialize instead of check_rotate_session.

* Update tests to new staking api.

* fixup mock

* Fix bond_extra_and_withdraw_unbonded_works.

* Fix bond_with_little_staked_value_bounded_by_slot_stake.

* Fix bond_with_no_staked_value.

* Fix change_controller_works.

* Fix less_than_needed_candidates_works.

* Fix multi_era_reward_should_work.

* Fix nominating_and_rewards_should_work.

* Fix nominators_also_get_slashed.

* Fix phragmen_large_scale_test.

* Fix phragmen_poc_works.

* Fix phragmen_score_should_be_accurate_on_large_stakes.

* Fix phragmen_should_not_overflow.

* Fix reward_destination_works.

* Fix rewards_should_work.

* Fix sessions_and_eras_should_work.

* Fix slot_stake_is_least_staked_validator.

* Fix too_many_unbond_calls_should_not_work.

* Fix wrong_vote_is_null.

* Fix runtime.

* Fix wasm runtime build.

* Update Cargo.lock

* Fix warnings.

* Fix grandpa tests.

* Fix test-runtime build.

* Fix template node build.

* Fix stuff.

* Update Cargo.lock to fix CI

* Re-add missing AuRa logs

Runtimes are required to know about every digest they receive ― they
panic otherwise.  This re-adds support for AuRa pre-runtime digests.

* Update core/consensus/babe/src/digest.rs

Co-Authored-By: DemiMarie-parity <48690212+DemiMarie-parity@users.noreply.github.com>

* Kill log trait and all that jazz.

* Refactor staking tests.

* Fix ci runtime wasm check.

* Line length 120.

* Make tests build again

* Remove trailing commas in function declarations

The `extern_functions!` macro doesn’t like them, perhaps due to a bug in
rustc.

* Fix type error

* Fix compilation errors

* Fix a test

* Another couple of fixes

* Fix another test

* More test fixes

* Another test fix

* Bump runtime.

* Wrap long line

* Fix build, remove redundant code.

* Issue to track TODO

* Leave the benchmark code alone.

* Fix missing `std::time::{Instant, Duration}`

* Indentation

* Aura ConsensusLog as enum

substrate/core/sr-primitives/src/generic/header.rs

@@ -21,9 +21,10 @@ use serde::Serialize;
 #[cfg(feature = "std")]
 use log::debug;
 use crate::codec::{Decode, Encode, Codec, Input, Output, HasCompact, EncodeAsRef};
-use crate::traits::{self, Member, SimpleArithmetic, SimpleBitOps, MaybeDisplay,
-	Hash as HashT, DigestItem as DigestItemT, MaybeSerializeDebug,
-	MaybeSerializeDebugButNotDeserialize};
+use crate::traits::{
+	self, Member, SimpleArithmetic, SimpleBitOps, MaybeDisplay, Hash as HashT, MaybeSerializeDebug,
+	MaybeSerializeDebugButNotDeserialize
+};
 use crate::generic::Digest;
 
 /// Abstraction over a block header for a substrate chain.
@@ -31,7 +32,7 @@ use crate::generic::Digest;
 #[cfg_attr(feature = "std", derive(Debug, Serialize))]
 #[cfg_attr(feature = "std", serde(rename_all = "camelCase"))]
 #[cfg_attr(feature = "std", serde(deny_unknown_fields))]
-pub struct Header<Number: Copy + Into<u128>, Hash: HashT, DigestItem> {
+pub struct Header<Number: Copy + Into<u128>, Hash: HashT> {
 	/// The parent hash.
 	pub parent_hash: <Hash as HashT>::Output,
 	/// The block number.
@@ -42,7 +43,7 @@ pub struct Header<Number: Copy + Into<u128>, Hash: HashT, DigestItem> {
 	/// The merkle root of the extrinsics.
 	pub extrinsics_root: <Hash as HashT>::Output,
 	/// A chain-specific digest of data useful for light clients or referencing auxiliary data.
-	pub digest: Digest<DigestItem>,
+	pub digest: Digest<<Hash as HashT>::Output>,
 }
 
 #[cfg(feature = "std")]
@@ -54,11 +55,10 @@ pub fn serialize_number<S, T: Copy + Into<u128>>(val: &T, s: S) -> Result<S::Ok,
 	::serde::Serialize::serialize(&(upper + lower), s)
 }
 
-impl<Number, Hash, DigestItem> Decode for Header<Number, Hash, DigestItem> where
+impl<Number, Hash> Decode for Header<Number, Hash> where
 	Number: HasCompact + Copy + Into<u128>,
 	Hash: HashT,
 	Hash::Output: Decode,
-	DigestItem: DigestItemT + Decode,
 {
 	fn decode<I: Input>(input: &mut I) -> Option<Self> {
 		Some(Header {
@@ -71,11 +71,10 @@ impl<Number, Hash, DigestItem> Decode for Header<Number, Hash, DigestItem> where
 	}
 }
 
-impl<Number, Hash, DigestItem> Encode for Header<Number, Hash, DigestItem> where
+impl<Number, Hash> Encode for Header<Number, Hash> where
 	Number: HasCompact + Copy + Into<u128>,
 	Hash: HashT,
 	Hash::Output: Encode,
-	DigestItem: DigestItemT + Encode,
 {
 	fn encode_to<T: Output>(&self, dest: &mut T) {
 		dest.push(&self.parent_hash);
@@ -86,16 +85,14 @@ impl<Number, Hash, DigestItem> Encode for Header<Number, Hash, DigestItem> where
 	}
 }
 
-impl<Number, Hash, DigestItem> traits::Header for Header<Number, Hash, DigestItem> where
+impl<Number, Hash> traits::Header for Header<Number, Hash> where
 	Number: Member + MaybeSerializeDebug + ::rstd::hash::Hash + MaybeDisplay + SimpleArithmetic + Codec + Copy + Into<u128>,
 	Hash: HashT,
-	DigestItem: DigestItemT<Hash = Hash::Output> + Codec,
 	Hash::Output: Default + ::rstd::hash::Hash + Copy + Member + MaybeSerializeDebugButNotDeserialize + MaybeDisplay + SimpleBitOps + Codec,
 {
 	type Number = Number;
 	type Hash = <Hash as HashT>::Output;
 	type Hashing = Hash;
-	type Digest = Digest<DigestItem>;
 
 	fn number(&self) -> &Self::Number { &self.number }
 	fn set_number(&mut self, num: Self::Number) { self.number = num }
@@ -109,23 +106,23 @@ impl<Number, Hash, DigestItem> traits::Header for Header<Number, Hash, DigestIte
 	fn parent_hash(&self) -> &Self::Hash { &self.parent_hash }
 	fn set_parent_hash(&mut self, hash: Self::Hash) { self.parent_hash = hash }
 
-	fn digest(&self) -> &Self::Digest { &self.digest }
+	fn digest(&self) -> &Digest<Self::Hash> { &self.digest }
 
 	#[cfg(feature = "std")]
-	fn digest_mut(&mut self) -> &mut Self::Digest {
+	fn digest_mut(&mut self) -> &mut Digest<Self::Hash> {
 		debug!(target: "header", "Retrieving mutable reference to digest");
 		&mut self.digest
 	}
 
 	#[cfg(not(feature = "std"))]
-	fn digest_mut(&mut self) -> &mut Self::Digest { &mut self.digest }
+	fn digest_mut(&mut self) -> &mut Digest<Self::Hash> { &mut self.digest }
 
 	fn new(
 		number: Self::Number,
 		extrinsics_root: Self::Hash,
 		state_root: Self::Hash,
 		parent_hash: Self::Hash,
-		digest: Self::Digest,
+		digest: Digest<Self::Hash>,
 	) -> Self {
 		Header {
 			number,
@@ -137,10 +134,9 @@ impl<Number, Hash, DigestItem> traits::Header for Header<Number, Hash, DigestIte
 	}
 }
 
-impl<Number, Hash, DigestItem> Header<Number, Hash, DigestItem> where
+impl<Number, Hash> Header<Number, Hash> where
 	Number: Member + ::rstd::hash::Hash + Copy + MaybeDisplay + SimpleArithmetic + Codec + Into<u128>,
 	Hash: HashT,
-	DigestItem: DigestItemT + Codec,
 	Hash::Output: Default + ::rstd::hash::Hash + Copy + Member + MaybeDisplay + SimpleBitOps + Codec,
  {
 	/// Convenience helper for computing the hash of the header without having