Refactor away from opaque hashes (#5226)

* System.BlockHash

* Fix hash

* Introduce K/V iteration in all _concat maps

Also move across:
- System.Account (blake2_128_concat)
- Balances.Locks (twox_64_concat)
- ElectionsPhragmen.VotesOf (twox_64_concat)
- ElectionsPhragmen.StakeOf (twox_64_concat)
- Identity.IdentityOf (twox_64_concat)
- Identity.SubsOf (twox_64_concat)
- Society.Payouts (twox_64_concat)
- Session.NextKeys (twox_64_concat)
- Identity.SuperOf (blake2_128_concat)
- Session.KeyOwner (blake2_128_concat)
- Society.SuspendedCandidates (twox_64_concat)
- Society.SuspendedMembers (twox_64_concat)
- Society.Vouching (twox_64_concat)
- Society.Strikes (twox_64_concat)
- System.EventTopics
- Balances.Account

* Build fixes

* Ensure migration happens in correct order

* Staking.*

* Vesting.* Offences.*

* Democracy.*

* Babe.* Collective.*

* Grandpa.*

* Assets.* Benchmark.* Contracts.* Elections.* Asset.* Nicks.*

Also introduce real account list

* ImOnline.*

* Treasury.*

* Recovery.*

* Final bits.

* Docs

* Fix one test

* Fix test

* All passing except the UI tests

* Remove linked_map part 1

* Remove linked_map

* Some iterator utils for double maps.

* Remove old migrations

* Introduce tombstone for LinkedMap type

* Migration for genesis hash

* Fix build

* Fix hash

* Rename Map is_linked -> unused, keeping backwards compat (#5256)

* Update frame/balances/src/lib.rs

Co-Authored-By: Shawn Tabrizi <shawntabrizi@gmail.com>

* Update frame/elections/src/lib.rs

Co-Authored-By: Shawn Tabrizi <shawntabrizi@gmail.com>

* Remove old migration code.

* Update frame/system/src/lib.rs

Co-Authored-By: Shawn Tabrizi <shawntabrizi@gmail.com>

* Update bin/node/runtime/src/lib.rs

Co-Authored-By: Shawn Tabrizi <shawntabrizi@gmail.com>

* Fix hash

* fix session migration

* Fix watning

Co-authored-by: Jaco Greeff <jacogr@gmail.com>
Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>
Co-authored-by: Robert Habermeier <rphmeier@gmail.com>

substrate/frame/session/src/historical.rs

@@ -56,12 +56,12 @@ decl_storage! {
 	trait Store for Module<T: Trait> as Session {
 		/// Mapping from historical session indices to session-data root hash and validator count.
 		HistoricalSessions get(fn historical_root):
-			map hasher(blake2_256) SessionIndex => Option<(T::Hash, ValidatorCount)>;
+			map hasher(twox_64_concat) SessionIndex => Option<(T::Hash, ValidatorCount)>;
 		/// The range of historical sessions we store. [first, last)
 		StoredRange: Option<(SessionIndex, SessionIndex)>;
 		/// Deprecated.
 		CachedObsolete:
-			map hasher(blake2_256) SessionIndex
+			map hasher(twox_64_concat) SessionIndex
 			=> Option<Vec<(T::ValidatorId, T::FullIdentification)>>;
 	}
 }
@@ -71,6 +71,20 @@ decl_module! {
 		fn on_initialize(_n: T::BlockNumber) {
 			CachedObsolete::<T>::remove_all();
 		}
+		fn on_runtime_upgrade() {
+			migration::migrate::<T>();
+		}
+	}
+}
+
+mod migration {
+	use super::*;
+	pub fn migrate<T: Trait>() {
+		if let Some((begin, end)) = StoredRange::get() {
+			for i in begin..end {
+				HistoricalSessions::<T>::migrate_key_from_blake(i);
+			}
+		}
 	}
 }