Introduce srml/im-online (#3079)

* Fix grammar and typo

* Extend network service

* Extend offchain API

* Support creating unsigned UncheckedExtrinsic

* Introduce srml/im-online

* Bump impl and spec version

* Fix web-wasm test

* Apply suggestions from code review

Remove parity-multiaddr dependency

Co-Authored-By: Pierre Krieger <pierre.krieger1708@gmail.com>

* Replace transmute with from_raw_parts

* Replace PeerId.to_string() with .to_base58()

Co-Authored-By: Pierre Krieger <pierre.krieger1708@gmail.com>

* Update Cargo.lock

* Bump impl and spec version (again)

It was updated in master in the meantime.

* Apply suggestions from code review

Co-Authored-By: Sergei Pepyakin <sergei@parity.io>

* Address comments

* Add public function is_online_in_current_session()

* Bump spec_version

* Fix doc tests

* Improve comments

* Remove superfluous line

* Name parameters consistently

* Implement comments

* Switch From to TryFrom

* Use Vec instead of HashSet

* Fix tests

* Revert me: local testing

* Fix check if already sent during session

We gossip each session, hence we need to check
if already sent in this session (not era).

* Fix typos

* Consistent terminology

* Revert "Revert me: local testing"

This reverts commit 73fbc29ff3e5ed71d99436318260b4f007e837f4.

* Introduce IsMember trait

* Implement misc comments

* Remove unused function

* Fix test

* Fix external_addresses being written

* Fix test

* Add necessary trait bound

* Do not increment version

* Update lib.rs

substrate/srml/aura/src/lib.rs

@@ -54,7 +54,7 @@ use rstd::{result, prelude::*};
 use parity_codec::Encode;
 use srml_support::{decl_storage, decl_module, Parameter, storage::StorageValue, traits::Get};
 use primitives::{
-	traits::{SaturatedConversion, Saturating, Zero, One, Member, TypedKey},
+	traits::{SaturatedConversion, Saturating, Zero, One, Member, IsMember, TypedKey},
 	generic::DigestItem,
 };
 use timestamp::OnTimestampSet;
@@ -210,6 +210,14 @@ impl<T: Trait> session::OneSessionHandler<T::AccountId> for Module<T> {
 	}
 }
 
+impl<T: Trait> IsMember<T::AuthorityId> for Module<T> {
+	fn is_member(authority_id: &T::AuthorityId) -> bool {
+		Self::authorities()
+			.iter()
+			.any(|id| id == authority_id)
+	}
+}
+
 /// A report of skipped authorities in Aura.
 #[derive(Clone, PartialEq, Eq)]
 #[cfg_attr(feature = "std", derive(Debug))]