Composite accounts (#4820)

* Basic account composition.

* Add try_mutate_exists

* De-duplicate

* Refactor away the UpdateBalanceOutcome

* Expunge final UpdateBalanceOutcome refs

* Refactor transfer

* Refactor reservable currency stuff.

* Test with the alternative setup.

* Fixes

* Test with both setups.

* Fixes

* Fix

* Fix macros

* Make indices opt-in

* Remove CreationFee, and make indices opt-in.

* Fix construct_runtime

* Fix last few bits

* Fix tests

* Update trait impls

* Don't hardcode the system event

* Make tests build and fix some stuff.

* Pointlessly bump runtime version

* Fix benchmark

* Another fix

* Whitespace

* Make indices module economically safe

* Migrations for indices.

* Fix

* Whilespace

* Trim defunct migrations

* Remove unused storage item

* More contains_key fixes

* Docs.

* Bump runtime

* Remove unneeded code

* Fix test

* Fix test

* Update frame/balances/src/lib.rs

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

* Fix ED logic

* Repatriate reserved logic

* Typo

* Fix typo

* Update frame/system/src/lib.rs

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

* Update frame/system/src/lib.rs

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

* Last few fixes

* Another fix

* Build fix

Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>
Co-authored-by: Jaco Greeff <jacogr@gmail.com>
Co-authored-by: Shawn Tabrizi <shawntabrizi@gmail.com>

substrate/bin/node/executor/tests/submit_transaction.rs

@@ -168,7 +168,7 @@ fn submitted_transaction_should_be_valid() {
 		let author = extrinsic.signature.clone().unwrap().0;
 		let address = Indices::lookup(author).unwrap();
 		let account = pallet_balances::AccountData { free: 5_000_000_000_000, ..Default::default() };
-		<pallet_balances::Account<Runtime, _>>::insert(&address, account);
+		<frame_system::Account<Runtime>>::insert(&address, (0u32, account));
 
 		// check validity
 		let res = Executive::validate_transaction(extrinsic);