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/staking/src/mock.rs

@@ -25,10 +25,8 @@ use sp_staking::{SessionIndex, offence::{OffenceDetails, OnOffenceHandler}};
 use sp_core::{H256, crypto::key_types};
 use sp_io;
 use frame_support::{
-	assert_ok, impl_outer_origin, parameter_types, StorageLinkedMap, StorageValue, StorageMap,
-	StorageDoubleMap,
-	traits::{Currency, Get, FindAuthor},
-	weights::Weight,
+	assert_ok, impl_outer_origin, parameter_types, StorageValue, StorageMap,
+	StorageDoubleMap, IterableStorageMap, traits::{Currency, Get, FindAuthor}, weights::Weight,
 };
 use crate::{
 	EraIndex, GenesisConfig, Module, Trait, StakerStatus, ValidatorPrefs, RewardDestination,
@@ -140,7 +138,7 @@ impl frame_system::Trait for Test {
 	type Version = ();
 	type ModuleToIndex = ();
 	type AccountData = pallet_balances::AccountData<u64>;
-	type OnNewAccount = ();
+	type MigrateAccount = (); type OnNewAccount = ();
 	type OnKilledAccount = ();
 }
 impl pallet_balances::Trait for Test {
@@ -373,7 +371,7 @@ pub fn check_exposure_all(era: EraIndex) {
 }
 
 pub fn check_nominator_all(era: EraIndex) {
-	<Nominators<Test>>::enumerate()
+	<Nominators<Test>>::iter()
 		.for_each(|(acc, _)| check_nominator_exposure(era, acc));
 }