Start handling P2P messages

This defines the tart of a very complex series of locks I'm really unhappy
with. At the same time, there's not immediately a better solution. This also
should work without issue.

coordinator/tributary/tendermint/src/ext.rs

@@ -263,6 +263,7 @@ pub trait Network: Send + Sync {
   /// Trigger a slash for the validator in question who was definitively malicious.
   ///
   /// The exact process of triggering a slash is undefined and left to the network as a whole.
+  // TODO: We need to provide some evidence for this.
   async fn slash(&mut self, validator: Self::ValidatorId);
 
   /// Validate a block.