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/srml/democracy/src/lib.rs

@@ -486,8 +486,6 @@ mod tests {
 		let mut t = system::GenesisConfig::<Test>::default().build_storage().unwrap().0;
 		t.extend(balances::GenesisConfig::<Test>{
 			balances: vec![(1, 10), (2, 20), (3, 30), (4, 40), (5, 50), (6, 60)],
-			transaction_base_fee: 0,
-			transaction_byte_fee: 0,
 			existential_deposit: 0,
 			transfer_fee: 0,
 			creation_fee: 0,