Add documentation to SubmitSignedTransaction and actually make it work (#4200)

* Add documentation to signed transactions and actually make them work.

* Fix naming and bounds.

* Forgotten import.

* Remove warning.

* Make accounts optional, fix logic.

* Split the method to avoid confusing type error message.

* Move executor tests to integration.

* Add submit transactions tests.

* Make `submit_transaction` tests compile

* Remove a file that was accidently committed

* Add can_sign helper function.

* Fix compilation.

* Add a key to keystore.

* Fix the tests.

* Remove env_logger.

* Fix sending multiple transactions.

* Remove commented code.

* Bring back criterion.

* Remove stray debug log.

* Apply suggestions from code review

Co-Authored-By: Bastian Köcher <bkchr@users.noreply.github.com>

* Make sure to initialize block correctly.

* Initialize block for offchain workers.

* Add test for transaction validity.

* Fix tests.

* Review suggestions.

* Remove redundant comment.

* Make sure to use correct block number of authoring.

* Change the runtime API.

* Support both versions.

* Bump spec version, fix RPC test.

Co-authored-by: Hernando Castano <HCastano@users.noreply.github.com>
Co-authored-by: Gavin Wood <github@gavwood.com>
Co-authored-by: Bastian Köcher <bkchr@users.noreply.github.com>

substrate/frame/im-online/src/lib.rs

@@ -171,10 +171,14 @@ pub type AuthIndex = u32;
 pub struct Heartbeat<BlockNumber>
 	where BlockNumber: PartialEq + Eq + Decode + Encode,
 {
-	block_number: BlockNumber,
-	network_state: OpaqueNetworkState,
-	session_index: SessionIndex,
-	authority_index: AuthIndex,
+	/// Block number at the time heartbeat is created..
+	pub block_number: BlockNumber,
+	/// A state of local network (peer id and external addresses)
+	pub network_state: OpaqueNetworkState,
+	/// Index of the current session.
+	pub session_index: SessionIndex,
+	/// An index of the authority on the list of validators.
+	pub authority_index: AuthIndex,
 }
 
 pub trait Trait: frame_system::Trait + pallet_session::historical::Trait {