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/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,
 	}
 }