Dispatch Calls to other modules (#1473)

* WIP

* Use system::Origin::Signed as an origin

* Add a vm test for ext_dispatch_call

* Take fee for dispatching a Call

# Conflicts:
#	node/runtime/wasm/target/wasm32-unknown-unknown/release/node_runtime.compact.wasm

* Clean & Rebuild

# Conflicts:
#	node/runtime/wasm/target/wasm32-unknown-unknown/release/node_runtime.compact.wasm

* Dispatch call test.

* Rebuild the runtime.

* Fix the length of the buffer.

* Rebuild binaries.

substrate/srml/contract/src/gas.rs

@@ -247,6 +247,13 @@ pub fn refund_unused_gas<T: Trait>(transactor: &T::AccountId, gas_meter: GasMete
 	<balances::Module<T>>::increase_total_stake_by(refund);
 }
 
+/// A little handy utility for converting a value in balance units into approximitate value in gas units
+/// at the given gas price.
+pub fn approx_gas_for_balance<T: Trait>(gas_price: T::Balance, balance: T::Balance) -> T::Gas {
+	let amount_in_gas: T::Balance = balance / gas_price;
+	<T::Gas as As<T::Balance>>::sa(amount_in_gas)
+}
+
 /// A simple utility macro that helps to match against a
 /// list of tokens.
 #[macro_export]