additional account relay list improvements

- Use the current selected account only to determine desired
  relays. Previously the desired relay list was determined from the
  union of all accounts.
- Update the relay configuration immediately when the user switches accounts.
- Delete relays from the account (instead of the relay pool
  directly). This results in the relay being removed in the pool as
  well, but is persisted correctly.

crates/notedeck_columns/src/relay_pool_manager.rs

@@ -41,6 +41,7 @@ impl<'a> RelayPoolManager<'a> {
         indices.iter().for_each(|index| self.remove_relay(*index));
     }
 
+    // FIXME - this is not ever called?
     pub fn add_relay(&mut self, ctx: &egui::Context, relay_url: String) {
         let _ = self.pool.add_url(relay_url, create_wakeup(ctx));
     }