Allow Substrate Pallet to be Halted (#485)

* Copy-Pasta owner and freezing code from `message-lane`

* Halt pallet if bridge hasn't been initialized

* Make owner optional in `message-lane` pallet

* Add `is_halted` to `InitializationData`

* Fix initialization tests

* Only allow pallet to be initialized once

* Add some logging around halting and ownership changes

* Remove `target` in debugging calls

bridges/bin/rialto/node/src/chain_spec.rs

@@ -187,5 +187,6 @@ fn load_kovan_bridge_config() -> Option<BridgeKovanConfig> {
 fn load_millau_bridge_config() -> Option<BridgeMillauConfig> {
 	Some(BridgeMillauConfig {
 		init_data: Some(rialto_runtime::millau::init_data()),
+		owner: Some([0; 32].into()),
 	})
 }

bridges/bin/rialto/runtime/src/millau.rs

@@ -32,6 +32,7 @@ pub fn init_data() -> InitializationData<Header> {
 		authority_list: authority_set.authorities,
 		set_id: authority_set.set_id,
 		scheduled_change: None,
+		is_halted: false,
 	}
 }