Fix tracking validator set in ImOnline (#3596)

* Use session::validators instead of staking::current_elected

* Basic test framework.

* Initialize validators, attempt to heartbeat.

* Use dummy crypto for im-online testing.

* Remove printlns.

* Finish test, make it invalid.

* Add reporting test.

* Finalize the test.

* Remove dumbness.

* Updates.

* Update AuRa

* Update srml/im-online/src/tests.rs

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

* Derive Ord

* Add some more tests.

* Remove stray todo.

* Bump runtime version.

* Bump impl-trait-for-tuples.

* Enforce new version of trait-for-tuples.

substrate/core/sr-primitives/src/lib.rs

@@ -56,7 +56,7 @@ pub use generic::{DigestItem, Digest};
 
 /// Re-export this since it's part of the API of this crate.
 pub use primitives::crypto::{key_types, KeyTypeId, CryptoType};
-pub use app_crypto::AppKey;
+pub use app_crypto::RuntimeAppPublic;
 
 /// Justification type.
 pub type Justification = Vec<u8>;