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/node/cli/src/chain_spec.rs

@@ -50,7 +50,7 @@ fn staging_testnet_config_genesis() -> GenesisConfig {
 	const CENTS: u128 = 1_000 * MILLICENTS;    // assume this is worth about a cent.
 	const DOLLARS: u128 = 100 * CENTS;
 
-	const SECS_PER_BLOCK: u64 = 4;
+	const SECS_PER_BLOCK: u64 = 6;
 	const MINUTES: u64 = 60 / SECS_PER_BLOCK;
 	const HOURS: u64 = MINUTES * 60;
 	const DAYS: u64 = HOURS * 24;
@@ -111,7 +111,7 @@ fn staging_testnet_config_genesis() -> GenesisConfig {
 			enact_delay_period: 0,
 		}),
 		timestamp: Some(TimestampConfig {
-			period: SECS_PER_BLOCK,
+			period: SECS_PER_BLOCK / 2, // due to the nature of aura the slots are 2*period
 		}),
 		treasury: Some(TreasuryConfig {
 			proposal_bond: Permill::from_percent(5),
@@ -234,7 +234,7 @@ pub fn testnet_genesis(
 			enact_delay_period: 0,
 		}),
 		timestamp: Some(TimestampConfig {
-			period: 5,                    // 5 second block time.
+			period: 2,                    // 2*2=4 second block time.
 		}),
 		treasury: Some(TreasuryConfig {
 			proposal_bond: Permill::from_percent(5),