Refactor: extract functions and types for creating extrinsics (#138)

* Extract extrinsic

* Extract extrinsic types to own module

* Fix compiler errors

* Fix warnings

* Fmt

* Pin wabt-sys to 0.7.1, it fails (on my machine) with 0.7.2

* Fix up tests

* Fmt

* Reexport RuntimeVersion

src/runtimes.rs

@@ -27,7 +27,7 @@ use sp_runtime::{
 };
 
 use crate::{
-    extra::{
+    extrinsic::{
         DefaultExtra,
         SignedExtra,
     },
@@ -40,7 +40,6 @@ use crate::{
         sudo::Sudo,
         system::System,
     },
-    Encoded,
 };
 
 /// Runtime trait.
@@ -51,20 +50,6 @@ pub trait Runtime: System + Sized + Send + Sync + 'static {
     type Extra: SignedExtra<Self> + Send + Sync + 'static;
 }
 
-/// Extra type.
-pub type Extra<T> = <<T as Runtime>::Extra as SignedExtra<T>>::Extra;
-
-/// UncheckedExtrinsic type.
-pub type UncheckedExtrinsic<T> = sp_runtime::generic::UncheckedExtrinsic<
-    <T as System>::Address,
-    Encoded,
-    <T as Runtime>::Signature,
-    Extra<T>,
->;
-
-/// SignedPayload type.
-pub type SignedPayload<T> = sp_runtime::generic::SignedPayload<Encoded, Extra<T>>;
-
 /// Concrete type definitions compatible with those in the default substrate `node_runtime`
 ///
 /// # Note