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/modules/substrate/src/storage.rs

@@ -38,6 +38,8 @@ pub struct InitializationData<H: HeaderT> {
 	pub set_id: SetId,
 	/// The first scheduled authority set change of the pallet.
 	pub scheduled_change: Option<ScheduledChange<H::Number>>,
+	/// Should the pallet block transaction immediately after initialization.
+	pub is_halted: bool,
 }
 
 /// A Grandpa Authority List and ID.