refactor: Transaction-Payment module (#3816)

* Initial draft that compiles

* Extract payment stuff from balances

* Extract multiplier update stuff from system

* Some fixes.

* Update len-fee as well

* some review comments.

* Remove todo

* bump

substrate/core/test-runtime/src/lib.rs

@@ -382,7 +382,6 @@ impl srml_system::Trait for Runtime {
 	type Lookup = IdentityLookup<Self::AccountId>;
 	type Header = Header;
 	type Event = Event;
-	type WeightMultiplierUpdate = ();
 	type BlockHashCount = BlockHashCount;
 	type MaximumBlockWeight = MaximumBlockWeight;
 	type MaximumBlockLength = MaximumBlockLength;