Offchain-worker APIs stubs (#2615)

* WiP: HTTP Apis.

* Working on the API.

* Add docs, clean up the API.

* Expose ext_ stuff as well.

* Implement HTTP helpers for offchain sr-io.

* Remove HTTP stuff.

* Revert "Remove HTTP stuff."

This reverts commit 7cca029d6ae93c5849b50edfcc6d2c313ba3e5bf.

* HTTP apis.

* Additional offchain methods.

* Make it compile.

* Implement wasm-ext boundary of offchain methods.

* Add stubs for offchain stuff to prevent panics.

* Fix tests.

* Addres some more issues.

* Introduce typedef, use unsafe from_utf8

* Bump runtime version.

* Introduce error to distinguish deadline and io errors.

* Add local_storage_cas

* Some tests for offchain stuff.

* Address more grumbles.

* Fix tests compilation.

* Fix borked merge.

* Improve docs for expected return values from ext functions.

* Adding new sign/enrypt/decrypt APIs.

substrate/core/primitives/src/lib.rs

@@ -56,6 +56,7 @@ pub mod ed25519;
 pub mod sr25519;
 pub mod hash;
 mod hasher;
+pub mod offchain;
 pub mod sandbox;
 pub mod storage;
 pub mod uint;
@@ -85,25 +86,11 @@ pub enum ExecutionContext {
 	/// Context used for block construction.
 	BlockConstruction,
 	/// Offchain worker context.
-	OffchainWorker(Box<OffchainExt>),
+	OffchainWorker(Box<offchain::Externalities>),
 	/// Context used for other calls.
 	Other,
 }
 
-/// An extended externalities for offchain workers.
-pub trait OffchainExt {
-	/// Submits an extrinsics.
-	///
-	/// The extrinsic will either go to the pool (signed)
-	/// or to the next produced block (inherent).
-	fn submit_extrinsic(&mut self, extrinsic: Vec<u8>);
-}
-impl<T: OffchainExt + ?Sized> OffchainExt for Box<T> {
-	fn submit_extrinsic(&mut self, ex: Vec<u8>) {
-		(&mut **self).submit_extrinsic(ex)
-	}
-}
-
 /// Hex-serialized shim for `Vec<u8>`.
 #[derive(PartialEq, Eq, Clone)]
 #[cfg_attr(feature = "std", derive(Serialize, Deserialize, Debug, Hash, PartialOrd, Ord))]