Keep network status & ring in a tokio::sync::watch

advantages
- reads don't prevent preparing writes
- can be followed from other parts of the system by cloning the receiver

src/server.rs

@@ -10,8 +10,8 @@ use tokio::sync::RwLock;
 
 use crate::api_server;
 use crate::background::*;
-use crate::data::*;
 use crate::block::*;
+use crate::data::*;
 use crate::error::Error;
 use crate::membership::System;
 use crate::proto::*;