Punish offline validators, aura-style (#1216)

* make offline-reporting infrastructure more generic

* add a listener-trait for watching when the timestamp has been set

* prevent inclusion of empty offline reports

* add test for exclusion

* generate aura-offline reports

* ability to slash many times for being offline "multiple" times

* Logic for punishing validators for missing aura steps

* stub tests

* pave way for verification of timestamp vs slot

* alter aura import queue to wait for timestamp

* check timestamp matches seal

* do inherent check properly

* service compiles

* all tests compile

* test srml-aura logic

* aura tests pass

* everything builds

* some more final tweaks to block authorship for aura

* switch to manual delays before step

* restore substrate-consensus-aura to always std and address grumbles

* update some state roots in executor tests

* node-executor tests pass

* get most tests passing

* address grumbles

substrate/srml/consensus/src/tests.rs

@@ -18,7 +18,7 @@
 
 #![cfg(test)]
 
-use primitives::{generic, testing, traits::OnFinalise};
+use primitives::{generic, testing, traits::{OnFinalise, ProvideInherent}};
 use runtime_io::with_externalities;
 use substrate_primitives::H256;
 use mock::{Consensus, System, new_test_ext};
@@ -63,3 +63,12 @@ fn authorities_change_is_not_logged_when_changed_back_to_original() {
 		});
 	});
 }
+
+#[test]
+fn offline_report_can_be_excluded() {
+	with_externalities(&mut new_test_ext(vec![1, 2, 3]), || {
+		System::initialise(&1, &Default::default(), &Default::default());
+		assert!(Consensus::create_inherent_extrinsics(Vec::new()).is_empty());
+		assert_eq!(Consensus::create_inherent_extrinsics(vec![0]).len(), 1);
+	});
+}