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/nicks/src/lib.rs

@@ -78,7 +78,7 @@ pub trait Trait: frame_system::Trait {
 decl_storage! {
 	trait Store for Module<T: Trait> as Nicks {
 		/// The lookup table for names.
-		NameOf: map hasher(blake2_256) T::AccountId => Option<(Vec<u8>, BalanceOf<T>)>;
+		NameOf: map hasher(twox_64_concat) T::AccountId => Option<(Vec<u8>, BalanceOf<T>)>;
 	}
 }
 
@@ -286,7 +286,7 @@ mod tests {
 		type Version = ();
 		type ModuleToIndex = ();
 		type AccountData = pallet_balances::AccountData<u64>;
-		type OnNewAccount = ();
+		type MigrateAccount = (); type OnNewAccount = ();
 		type OnKilledAccount = ();
 	}
 	parameter_types! {