Add logout button, and show account keys

Changelog-Added: Show logout button and account keys in config
Signed-off-by: William Casarin <jb55@jb55.com>

damus/damusApp.swift

@@ -35,6 +35,9 @@ struct MainView: View {
                     }
             }
         }
+        .onReceive(handle_notify(.logout)) { _ in
+            keypair = nil
+        }
         .onAppear {
             keypair = get_saved_keypair()
         }