* SignedBlock: get justification by consensus engine id
* Define ConsensusLogReader
Making the check for authority changes more generic
* cod review changes
* Decouple `relays/client-substrate` from `headers_relay`
* Remove `blocks_in_state` from `SyncLoopMetrics`
This metric was only relevant for PoA <> Substrate bridge.
* Move `sync_loop_metrics.rs` to `relays/finality`
* Remove unused `SyncLoopMetrics::update()`
* Hook up SyncLoopMetrics to finality_loop
* Delete now unused `relays/headers`
Signed-off-by: acatangiu <adrian@parity.io>
Serban Iorga