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/frame/generic-asset/src/mock.rs

@@ -31,7 +31,7 @@ use frame_support::{parameter_types, impl_outer_event, impl_outer_origin, weight
 use super::*;
 
 impl_outer_origin! {
-	pub enum Origin for Test  where system = frame_system {}
+	pub enum Origin for Test where system = frame_system {}
 }
 
 // For testing the module, we construct most of a mock runtime. This means
@@ -62,6 +62,9 @@ impl frame_system::Trait for Test {
 	type BlockHashCount = BlockHashCount;
 	type Version = ();
 	type ModuleToIndex = ();
+	type AccountData = ();
+	type OnNewAccount = ();
+	type OnReapAccount = ();
 }
 
 impl Trait for Test {
@@ -77,6 +80,7 @@ mod generic_asset {
 use frame_system as system;
 impl_outer_event! {
 	pub enum TestEvent for Test {
+		system<T>,
 		generic_asset<T>,
 	}
 }