Contracts: clean (#788)

* Extract `runtime` module

* Restructure & comment code to avoid confusion

substrate/srml/contract/src/exec.rs

@@ -90,6 +90,7 @@ impl<'a, T: Trait> ExecutionContext<'a, T> {
 						ctx: &mut nested,
 						_caller: caller,
 					},
+					&::vm::Config::default(),
 					gas_meter,
 				).map_err(|_| "vm execute returned error while call")?;
 			}
@@ -154,6 +155,7 @@ impl<'a, T: Trait> ExecutionContext<'a, T> {
 					ctx: &mut nested,
 					_caller: caller,
 				},
+				&::vm::Config::default(),
 				gas_meter,
 			).map_err(|_| "vm execute returned error while create")?;