Transaction Fee Module (#1648)

* wip

* Split bytes fee charging and charging by amount into different traits.

* Move to edition 2018.

* Implemented charge fee traits for fees module.

* Implemented 'on_finalise' for fee module.

* Updated fees finalize impl.

* Renaming and documentation update.

* Added overflow & underflow check for fee calculation.

* Added mock and unit tests for fee module.

* More unit tests for fees module.

* Fixed srml-executive unit tests.

* Remove transaction base/bytes fee from balances module, fix unit tests.

* fix compile error

* Fixed unit test.

* Minor fixes.

* Bump spec version.

* Bump spec version.

* Updated fees module and runtime wasm.

* Fees module code style improvement; updated runtime wasm.

* Bump spec and impl version.

substrate/node-template/runtime/src/lib.rs

@@ -164,6 +164,12 @@ impl balances::Trait for Runtime {
 	type Event = Event;
 }
 
+impl fees::Trait for Runtime {
+	type Amount = u128;
+	type TransferAsset = Balances;
+	type Event = Event;
+}
+
 impl sudo::Trait for Runtime {
 	/// The uniquitous event type.
 	type Event = Event;
@@ -188,6 +194,7 @@ construct_runtime!(
 		Indices: indices,
 		Balances: balances,
 		Sudo: sudo,
+		Fees: fees::{Module, Storage, Config<T>, Event<T>},
 		// Used for the module template in `./template.rs`
 		TemplateModule: template::{Module, Call, Storage, Event<T>},
 	}
@@ -208,7 +215,7 @@ pub type UncheckedExtrinsic = generic::UncheckedMortalCompactExtrinsic<Address,
 /// Extrinsic type that has already been checked.
 pub type CheckedExtrinsic = generic::CheckedExtrinsic<AccountId, Nonce, Call>;
 /// Executive: handles dispatch to the various modules.
-pub type Executive = executive::Executive<Runtime, Block, Context, Balances, AllModules>;
+pub type Executive = executive::Executive<Runtime, Block, Context, Fees, AllModules>;
 
 // Implement our runtime API endpoints. This is just a bunch of proxying.
 impl_runtime_apis! {